Ancient Mysteries - The Massive Underground Cities We Weren’t Supposed to Find

Episode Date: August 22, 2026

Entire cities were built beneath the ground — hidden from armies, invaders, extreme climates, and sometimes from history itself.In this documentary, we journey beneath the surface to explore some of the world's most extraordinary underground settlements and structures.From the vast underground city of Derinkuyu in Turkey to hidden tunnels beneath France, ancient complexes discovered beneath modern towns, ingenious underground infrastructure, and remarkable structures carved directly into solid rock, these places reveal just how far civilizations were willing to go to survive — and sometimes to disappear.How were thousands of people able to live beneath the surface? How did they get fresh air and water? And perhaps most intriguing of all: how many underground places could still be waiting to be discovered?Join us as we explore the engineering, history, discoveries, and mysteries of the incredible worlds built beneath our feet.💬 Which underground city would you want to explore?🔔 Subscribe for more documentaries about lost civilizations, remarkable discoveries, ancient engineering, and the mysteries hidden throughout history.

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by J.D. Power is designed for your everyday and with available all-wheel drive you can handle your to-do list with total confidence. Start your build at chevrolet.ca. Details at J.D.Power.com Hey there, history lovers. Turkey, 1963. A farmer knocks down a wall in his basement, just a guy fixing a damp corner. Behind the wall there is no room. There is cold air and a passage dropping 85 metres into an 18-level city built for 20,000 people. And he was not alone in finding one. Cultures that never met,

separated by oceans and thousands of years, all reached the same conclusion. Stop building up, start cutting down, brutal work because you're not stacking stones, you're deleting a mountain. And there is no undo button. Why did they do it? To hide, to survive, to pray, usually all three at once. Hit that like button if this is your kind of deep dive and drop a comment telling me what city you're watching from. Let's go down. Our first stop does not look like a stop at all. Northern France, the region of Picardy, an hour or so from the coast, and you're standing on farmland so aggressively ordinary

that your brain refuses to file it under anything but wheat. Gentle hills, a church tower, a village of a few hundred people called Nauze, the kind of place where the big weekly event is the bread van. There is no ruin here, no dramatic cliff, no sign saying something extraordinary happened on this spot. That is not an accident. that is the entire design goal. Because roughly 20 to 30 metres under those wheat fields sits a hidden settlement of almost 300 rooms,

more than two kilometres of tunnels arranged into 28 separate galleries, and enough space to swallow 3,000 people along with their animals, their grain and their extremely stressed grandmothers. To understand why anyone would do this, you have to understand the geography, which is a polite way of saying you have to understand the bad luck. Picardy sits on the flat open corridor, between Paris and Flanders, which for about a thousand years functioned as the express lane for every army in Western Europe. Anyone marching to attack anyone else came through

here, and armies of that era did not exactly stop at the border for a customs declaration. They lived off the land, and the land in question was somebody's farm. Vikings came up the rivers, English armies came through during the Hundred Years' War, Spanish and Imperial troops came through during the wars of religion, and there were mercenary bands who were technically nobody's army at all, which somehow made them worse, because at least a real army occasionally had a commander who wanted the village intact for tax purposes. Freelancers had no such long-term thinking, so the peasants of Picardy did the math. You cannot fight cavalry with a hoe. You cannot outrun horses on foot while carrying a pig. Building a wall around your village is

illegal, expensive, and honestly just advertising that you own things worth stealing. What you can do is disappear. And underneath their feet was the answer. because this whole region is built on chalk. Chalk is a wonderful material with one very funny personality trait. It is soft enough to carve with hand tools, which means a farmer with a pit can genuinely excavate a room in a few weeks rather than a few decades. It hardens slightly on contact with air, so what you cut tends to stay cut. It is dry and stable in a way that clay absolutely is not. The catch is that chalk hates water and it hates sharp corners. Cut a square room with a flat ceiling, and you have just built a very heavy,

stone slab with nothing under the middle of it, and the plateau above will eventually remind you that gravity has a perfect attendance record, which is why every significant chamber down there is rounded, arched, vaulted, gently curved, the walls flowing into the ceiling. That geometry pushes the load outward and sideways into the mass of rock instead of straight down onto empty air. Nobody in the 1300s had a formula for compressive stress distribution. They just had a very direct feedback system, where wrong answers were fatal, which turns out to be an extremely effective teaching method. The excavation itself started long before the crisis years. Parts of the network were almost certainly quarries first, since Roman and later medieval builders were cutting chalk blocks

out of these hills for construction, and the useful thing about a quarry is that it comes pre-installed with an entrance nobody thinks about. Later generations took those industrial leftovers and turned them into something else entirely, what began as a whole where the building material used to be became a place to put the people. And here is where it stops being a cave and starts being a town, because the layout is not random. There are streets, in the sense of main galleries with smaller passages branching off them. There are rooms assigned by household, which means somebody had to allocate them, which means there was underground bureaucracy, which means that even inside a secret refuge from marauding soldiers, there was almost certainly an argument about whose family got the bigger

room. There are stables cut into the rock for cattle and horses, because leaving your livestock on the surface is the same as leaving a note that says we're hiding nearby. Help yourself. There are wells reaching the water table, so the population did not have to send someone upstairs with a bucket at the worst possible moment. There are stone benches, storage niches and fireplaces. There are chapels, plural, complete with carved altars, because a medieval French village faced with the end of the world was not going to skip mass over something as minor as being underground. Now we get to the part that I think is the genuinely brilliant piece of engineering and it has nothing to do with digging. Any idiot can hide in a hole. The hard part is hiding the evidence

that a hole is occupied. 3,000 people breathe, they cook, they light fires for warmth, because the temperature down there is a constant and clammy handful of degrees above freezing, all year, forever. Fire makes smoke, and smoke is the single most reliable snitch in human history. A column of smoke rising out of a hillside in the middle of empty farmland does not say nothing to see here. It says free food and prisoners this way. The solution at Nowes is the kind of thing that makes you want to shake the hand of a dead peasant. The ventilation shafts were driven upward through the chalk for tens of meters, and then deliberately vented in places where smoke does not read as smoke.

Some outlets came out in the middle of dense woodland. where the plume broke apart in the canopy and dispersed into what looks at dawn, exactly like ordinary mist sitting in the trees. Others were connected directly into the chimneys of houses in the village on the surface, so the smoke from the hidden kitchens came out of a perfectly normal chimney on a perfectly normal cottage that was already smoking anyway. A patrol riding past sees a village going about its business. It does not see the fact that the fire producing that smoke is 200 metres away and 20 metres

underground with several hundred people gathered around it holding their breath. That is not hiding. That is misdirection. That is a village performing an impression of itself while the real version waits below, and it worked so well for so long that the network kept expanding across centuries. The full complex we can walk through today is the accumulated work of generations, each one inheriting the tunnels, adding rooms, and passing the whole thing down like a very strange family heirloom that you hope nobody ever needs to use. Then, in the 1700s, the authorities decided that a hidden fortress capable of concealing thousands of people was an interesting thing for a rural population to have lying around, which from a government perspective is a fair concern,

since anything that can hide refugees can also hide smugglers, deserters, tax evaders, and people with opinions. The entrances were sealed, and that should have been the end of it. Communities move on. memory phrase, the grandchildren of the last people to use the tunnels grew up hearing stories about caves under the fields, the way we hear stories about a cousin who supposedly met a celebrity once. It was a local priest, Abed Anikor, who went looking in the 1880s on the strength of those half-remembered stories and old records, and reopened the network. Imagine the professional confidence required. You are the village priest. You have announced that you intend to find a lost city under the parish. There is no scenario in which you are you. You are the village priest. You have announced that you intend to find a lost city under the parish.

There is no scenario in which you look good if the answer is a few muddy holes. Fortunately for him, the answer was several hundred rooms, which brings us to the layer of this place that nobody planned and nobody could have predicted, and it is the reason Naos went from a regional curiosity to an international story about a hundred years later. The walls are covered in writing. More than 3,000 individual inscriptions were catalogued during a detailed survey carried out across 2014 and 2015. and the earliest of them are exactly what you would expect. Medieval and early modern names, dates, crosses, symbols,

the marks of people who came down here because the alternative was worse and who wanted the rock to remember they existed. Graffiti is not vandalism when it is the only writing surface available to people who own nothing. But scattered through all of that in fresh pencil and carved letters are names like the ones you would find on a rugby team sheet from 1916. British names, Australian names, regiment numbers, hometowns written out in careful block capitals. Because Naos sits a short march behind the front line of the Somme, and during the First World War the tunnels were not a refuge at all. They were a tourist attraction. Take a second with that.

Soldiers rotated out of the trenches for a few days of rest, handed a break from the loudest and worst environment human beings have ever manufactured, and what did they choose to do with their free afternoon. They went and looked at the local underground town. It was already a known local site by then. Someone was charging admission, and men who had spent weeks living in mud corridors under artillery fire paid money to go and walk through a different set of corridors, voluntarily, as a day out. That is either the most cheerful thing you will hear today or the bleakest, depending entirely on your mood. And then they signed the walls. Not as a statement, not for history. They signed the way any group of bored young men signed anything, because it was there, because

their friends were doing it, because writing your name and your unit and the town you came from is the most basic possible way of saying I was a person and I was in this place on this date. Many of them wrote their full home address, which is heartbreakingly optimistic, like leaving a forwarding address for a future that had not been confirmed yet. The researchers who documented those names were able to match a large number of them to service records which means we can trace individual men from a scratch on a chalk wall in Piccadie to their regiment, their movements, and in far too many cases the field where the rest of their story ended a few kilometres away.

A soldier from Adelaide who had never seen a chalk plateau in his life stood in a room carved by French farmers, escaping cavalry raids 400 years earlier, and left a mark next to theirs, and had absolutely no idea he was continuing a conversation. That is what makes this first stop the right one. Naur is not the biggest thing we are going to see, not by a wide margin, and it is not the deepest or the most ornate. What it is is the clearest possible statement of the first motive.

These people did not go into the rock because it was comfortable. It was cold, it was dark, it smelled like several hundred humans, and their cattle sharing a poorly ventilated basement, and nobody down there was enjoying themselves. They went in because the ground was the only thing in Pickety that armies could not steal, burn or ride through. The surface belonged to whoever showed up with the most horses. The dark belonged to whoever knew where the door was, which sets up the obvious question. If a few thousand French peasants could hollow out a hiding place this sophisticated with hand tools and stubbornness,

what happens when a much larger population, sitting on much better rock, spends much more time on the problem and needs to hide not for a week but for years at a stretch? For that we go to Turkey and we go a great deal further down. The answer to that question, is sitting under a dusty town in central Anatolia, and the town is called Derinkyu, which in Turkish means deep well. That is the actual name. The people living on top of this thing named their home,

after the fact that the holes go down a long way, which has to be the single most understated place name in the history of human settlement. It is like calling a town big hole and then acting surprised when someone finds an 18-level metropolis under the grocery store. We already met the moment it came back into the world in the 1960s, so let us skip ahead to what was actually waiting down there, because the numbers do not really process on first contact. 85 metres of vertical depth, 18 distinct levels. Capacity estimates that run as high as 20,000 people, and that figure is not just bodies, it includes their livestock, their food stores, their oil, their wine, and everything else

required to keep a functioning society alive while the world above them was busy being a war zone. 20,000 people is a decent-sized town today. Now put that town in a stack, underground, in the dark, and give it one job. Do not be found, and if found, do not be entered. None of this happens without the rock, and the rock here is the reason Capadocia looks like a fever dream in the first place.

Millions of years ago, the volcanoes in this region, including the enormous Euseas, buried the whole landscape in layers of ash. That ash compacted into tough, which is the geological equivalent of a material specifically manufactured for this purpose. It is soft enough that a determined person with an iron pick can carve it like hard cheese, and then, on exposure to air, the cut surface hardens into a durable shell, so you dig fast and the result gets stronger over time.

Compare that to the situation in Picardy, where the material cooperates but sulks the moment it gets damp, and you start to see why one region produced a hiding place, and the other produced an entire underground civilization. Same human instinct. Wildly different budget. Nobody can tell you with certainty who started it. The most commonly cited theory credits the Frigians

somewhere around the 8th or 7th century before the common era, others point further back, and honestly the disagreement is built into the problem because carving a hole leaves no foundations, no rubbish layer, and no construction debris to date. When you build a castle, you leave evidence of the building. When you carve a city you leave absence, and absence is notoriously bad at answering questions. What is clear is that whoever started it, the later residents inherited it,

and immediately did what humans always do with inherited property, which is renovate aggressively and add an extension. The people who turned it into what we see now were Byzantine-era Christians, and their motivation was extremely specific. From the 7th century onward, the frontier between the Byzantine world and the expanding Arab caliphates ran straight through this landscape, and raiding season became an annual fixture of life, roughly as reliable as harvest and considerably less enjoyable. Later came Mongols, later still came other pressures, and the pattern held for over a thousand years. A warning arrives,

and a whole region goes into the ground and closes the lid. Which is why the layout is not a maze, it is a filing system. The top levels held the animals. This sounds like laziness, and it is actually thermodynamics with the side of common sense. Nobody wanted to march a cow down 12 flights of carved staircase, which as a logistical exercise ranks somewhere between impossible and comedy. But more importantly, animals are furnaces. A stable full of livestock generates a serious amount of body heat and heat rises, so the herd on the upper floors was quietly warming the floors above them for free, while the smell and the waste stayed at the top where it could be pushed out rather than settling on top of the entire population. Their dung was also collected and dried as fuel,

because down here nothing was wasted, and there was certainly no woodland delivery service. Naturally, the family assigned to stable duty had the worst job in the city, and there is no record of anyone volunteering. Go down a few levels, and the function changes completely. This is the industrial floor, kitchens with ceilings still blackened by soot, communal ovens, wine presses cut directly into the rock with channels and collection basins, oil presses working the same way, and storage rooms lined with enormous jars. The presses are the detail that tells you these people were not planning a long weekend. You do not carve a permanent winery into a refuge unless you expect to be processing an actual harvest in it. The grapes came down, the wine stayed down. This was not an

emergency shelter, it was a second address, and a fully equipped one at that. Below the workshops, the rooms turn residential and then turn sacred, and on the seventh level you reach the piece that gets people quiet when they see it. A church, carved in a cross-shaped plan, with a barrel-vaulted ceiling and columns that hold up nothing, because in a carved building no column is ever structural. It is a shape the builders chose to leave behind out of solid stone, for no reason, except that a church is supposed to look like a church. Somebody stood in the dark 60 metres under the fields, and decided that the vault needed to curve properly. That is not engineering.

That is stubbornness with a religious motive, and it is the most human thing in the entire complex. There is also a long barrel-vaulted hall on one of the levels, often described as a school, complete with side rooms interpreted as study spaces, which means that at some point in history there was a child, underground, being told to pay attention, while an army rode around overhead.

Some experiences are truly universal. Now the security system, and this is where the design gets genuinely clever rather than merely impressive, the threat model was not a siege. Nobody was going to besiege a city they could not see. The threat was a raiding party, finding an entrance and coming in, so the entire defensive logic is built around corridors, and the corridors are the weapon. They are deliberately narrow and low, forcing anyone moving through them to go single file and hunched over, which strips an attacker of every advantage he has. formation, no shield wall, no swinging a sword sideways, no bringing eight friends. You get one man,

bent double in the dark, in a passage he does not know, and behind him is another man in exactly the same helpless position, who cannot help him and cannot get past him, and then he reaches a door. The famous round stone doors of Dering QU are millstone-shaped discs of hard rock, some of them approaching half a ton, sitting in a carved recess beside the passage. They roll across the corridor and seal it. From the inside, a few people using a lever and the natural groove can move one into place. From the outside, in a passage too narrow to get more than one person against it, with nothing to grip and no leverage, it is effectively a mountain that says no. There is no handle, there is no mechanism, there is nothing to break. It is a plug the size of a car tire made of solid rock,

and the physics of the corridor are doing the defending as much as the door is. The best part is the hole. Each disc has a circular opening through the same. center, and the practical explanations are the good ones. It lets the defenders see who is on the other side, which is preferable to guessing. It provides a fixed point to work the door with a beam, and it gives you a clean firing slot straight down the axis of a corridor, where the enemy has no ability to dodge, because the corridor is one person wide. It is a peephole with an offensive capability, which is essentially the medieval version of a security camera that can also stab you. And because layered defense is the whole philosophy here, there is not one of these

doors. There are many, at multiple levels, so that breaching one earns an attacker nothing except a slightly deeper position. In a tunnel system, he does not have a map for, with the local population sealed off below him, calmly waiting for him to run out of light and patience, which brings us to the actual thing that decides whether an underground city lives or dies, and it is not the doors, it is air. Threaded through the entire complex are more than 50 ventilation shafts, and the main one drops roughly 55 metres. This is the spine of the place. The temperature difference between the deep levels and the surface drives a constant convection current, pulling stale air up and drawing fresh air down through the network, which is how 20,000 people plus a herd of livestock plus hundreds of burning oil

lamps do not asphyxiate themselves within a day. Every one of those little flames is competing with a human being for oxygen, and the shafts are the only reason that competition stays winnable. but the main shaft has a second job, and it is the detail I find most quietly ruthless. It also functions as the city's well, reaching down to the water table, and critically, at certain points in the design, the water source was kept sealed from above, deliberately not accessible from the surface. Think about what that means. The builder sat down and asked themselves what a determined enemy would do if he knew people were hiding underground but could not get at them,

and they came up with the correct answer, which is poison the water, and weight. So they designed the supply so that the only access was from the inside, the people up top could stand directly over the well and be unable to touch it. That is not a construction decision. That is somebody modelling the mind of an enemy who has not arrived yet, and building the counter into the geology. Life inside was not a charming rustic experience. It was cold, it was permanently dark, the air was thick with lamp smoke and the smell of several thousand people, and their animals sharing an enclosed volume, and communities are known to have stayed under for weeks, and in some cases considerably longer. There were dedicated spaces for the

dead, because in a sealed environment you cannot exactly hold a funeral procession, and there were niches for lamps in every passage, because losing your light in there was not an inconvenience, it was a genuine emergency. And there was a tunnel, several kilometres long, connecting Dering QU to the neighbouring underground city of Chemakli, which means these were not isolated shelters at all, but nodes in a network, capable of moving people and supplies between towns entirely below the surface. The region above ground could be completely occupied, while the region below ground continued operating normally, which is a strategic situation most invading armies never even considered as a possibility. The complex stayed in use in some form for an astonishingly long time,

with the local Greek-speaking capital-coctocean population still going underground, during periods of danger well into the modern era, right up until the population exchange of the early 1920s emptied the region of the communities who knew how the place worked. And that is the mundane, slightly deflating truth about how a city this size gets forgotten. Nobody buried it. Nobody sealed it in a dramatic ceremony. The people who held the knowledge simply left, a knowledge that lives in heads and habits rather than in books evaporates in about one.

generation. Forty years later, a man knocked down a wall, which raises the obvious and slightly unsettling follow-up, if a complex of this scale could sit forgotten under an inhabited town until an accident revealed it, how many more accidents are still waiting? As it happens, we do not have to speculate because one of them happened in 2020, under the streets of a completely different Turkish town, and what came out of the ground there may end up making Derengueu look modest. southeast in Turkey, near the Syrian border, on a limestone plateau called Turabdin. The town is Midiat, and it is genuinely lovely in a way that has nothing to do with archaeology. Honey-coloured stone houses, carved facades, church towers, a skyline that has barely changed in centuries.

Around 2020, the local authorities launched exactly the kind of project that put city councillors to sleep in every country on earth, tidy up the historic quarter, bury the ugly overhead cables, clean up the streets, restore some of the older buildings, municipal improvement works, the least glamorous phrase in any language, and then somebody went into a cellar and found a hole in the wall. Behind the hall was a passage, behind the passage was a room. Behind that room was another corridor, and another room and a staircase, and a water cistern, and a chamber cut for worship, and the growing realisation among everyone present that the street cleaning project had just been upgraded into something else entirely.

What they had walked into is now called Matyate, and here is the detail that makes the whole story delicious. Matiate is not a modern invention. It is an ancient name meaning city of caves, and it appears in Assyrian records going back to the 9th century before the common era. It is also, with a bit of linguistic erosion over 3,000 years, where the modern name Midiat comes from. Read that again. The town has been called the city of caves this entire time. The clue was not buried. It was on the road signs.

Everyone who has ever mailed a letter to Midiat has been writing the answer on the envelope for generations, and nobody thought to ask why, because that is not how place names work in daily life. Two and five Canadians will hear the words, you have cancer. That's why every step and dollar raised matters. On September 19th, joined thousands in Toronto for the Princesses. Margaret Cancer Foundation Walk. Challenge yourself, friends, and family to walk 21 kilometers in support of life-saving research.

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there's a Volvo for everyone. Learn more at VolvoCars.a. Nobody in Oxford wonders about the ox or the Ford either. What has come out of the ground since is still, and this is the important part, only the beginning. The excavated portion includes dozens of chambers linked by carved corridors, and the teams working the site have been consistently clear that they have opened a very small fraction of the total, a single-digit percentage. The rest is still under the houses, under the streets, under the shops, under people who are currently going about their day with no particular thoughts about their basement. The projected full extent, based on how far the corridors run before they hit unexcavated fill,

is enormous. Some of the figures that have been floated for the eventual size and population capacity are frankly extravagant, ranging into the tens of thousands of inhabitants, and I would treat those numbers with a healthy pinch of salt for now, because an estimate produced when you have opened 5% of something is not a measurement, it is an educated guess wearing a confident expression. But even the cautious readings point to a complex that could comfortably outclass anything else in the country, including the 18-level giant we just came out of. Now, the rock. Turabdin is limestone country, and limestone is not the friendly volcanic material of Cappadocia. It is harder, it is more stubborn, it dulls tools, and it does not offer that convenient

trick of softening on the way in and hardening afterwards. Carving a city here is significantly more labour per cubic metre, and that changes the meaning of the whole project. When digging is easy, a big excavation might just reflect available time. When digging is this difficult, every chamber represents a decision somebody made while sweating, with a blunt chisel, having already asked themselves whether it was really worth it. The scale of Matyatta is therefore not a measure of ambition, it is a measure of desperation. Which brings us to who and when, the current dating places the earliest used somewhere around

the second and third centuries of the common era, and the leading interpretation is that the first residents were early Christian and Jewish communities living under Roman rule, at a time when both were, depending on the emperor and the decade, either tolerated, taxed, harassed or actively hunted. This is well before Christianity became the officially approved religion of the empire, and the practical experience of being an early believer in a provincial town was less about theological debate and more about the extremely unpleasant question of what happens when the authorities decide this month is a good month for making an example of somebody. So you can see the logic assembling itself. You are a minority community. You cannot leave

because your land, your family and your entire livelihood are here. You cannot fight because the opposition is the Roman army, and that is not a fight, that is a formality. You cannot argue in court because the court is the problem. What you can do is take the one asset nobody has thought to regulate, which is the rock directly beneath your house, and turn it into a place where you and your neighbours can simply stop existing for a while. And the archaeology fits that reading beautifully.

There are cisterns, cut to collect and hold water, There are silos for grain. There are chambers that appear to have served as places of worship, including one with a carved star of David on the wall, which is the sort of fine that immediately turns a hole in the ground into a document. There are rock-cut graves. There are the bones of both people and animals, which tells you livestock came down with the population, exactly as we saw elsewhere, because a farm animal left standing in the yard is a signed confession. There are oil lamps and coins, the ordinary rubbish of ordinary occupation. This was not a shrine or a tomb complex that later got repurposed. People lived here, ate here, prayed here, and stored a season's

food here. What makes Matiata structurally different from the Kapadocian model is the relationship with the surface. Derinkuyu is a separate world that happens to be underneath a town. Matiatt reads more like a shadow copy of the town itself, with entrances directly through the cellars and courtyards of houses, a private trapdoor arrangement rather than a set of grand communal gates. That is a fundamentally different security philosophy. Instead of one hardened fortress with layered choke points, you get a distributed system with dozens of independent doorways, meaning there is no single entrance to guard, and more importantly, no single entrance for an enemy to find. Kick in one house and you have found one cellar.

The neighbours are already gone through their own hatch into a network that connects underneath the street you're standing on. It also means the transition from surface life to underground life could be almost instantaneous. No march to a shelter outside town, no visible movement of families across open ground. Word arrives, and a community of hundreds evaporates from their homes in the time it takes to walk downstairs. There is a strong argument that the site kept getting reused long after the original crisis passed, which is what always happens to good real estate, even the kind with no windows. Once the danger receded, chambers that had been designed for hiding became storage, workshops, cellars, catacombs. Later generations kept some of it in casual use

and gradually forgot what the rest of it was, until the connecting corridors were bricked up, filled with rubble, or simply lost behind a wall somebody built in the 1600s because they wanted a bigger pantry. That is not a mystery, that is just property maintenance operating on a year time scale. And that is really the point of this stop. And the reason it belongs here rather than as a footnote. We have a comfortable mental model of archaeology in which the discoveries happen somewhere remote, a jungle, a desert, under a lake, behind a landslide, at the bottom of the sea, somewhere that requires an expedition, ideally with a hat. Matiatt does not fit that model at all, because Matyat was found under a functioning town, beneath the floors of houses where

families were eating dinner, under streets with cars parked on them, under shops with normal opening hours, there was no expedition, there was a work crew with a permit, which forces the uncomfortable question. If a city of this size can sit undetected under an inhabited town in a well-study part of a country with an exceptionally strong archaeological tradition, until a routine street project accidentally opened a wall, then what is the actual likelihood that this is the last one? The honest answer is somewhere between low and comically low. Turkey alone has hundreds of known underground settlements, and the strong suspicion is that the known ones are the ones with an entrance that never quite closed.

Everything else is waiting for a burst pipe, a new car park, or a homeowner who wants a wine cellar. Excavation at Matiata is ongoing and slow, and slow is correct here, because unlike a field site, there is a town on top. You cannot open the ceiling of a chamber if the ceiling is somebody's living room floor, so progress is measured in careful metres rather than dramatic reveals, and the full map may take decades. In the meantime, the residents of Midiat get to live with a genuinely surreal knowledge that their address has a second, older version of itself directly below, and that the two versions are separated by a few metres of limestone and about 1800 years.

So that closes out the first motive, and it closes it with a pattern that repeats across every continent. Fear is a fantastic architect. three separate communities with nothing in common except a threat they could not defeat, all arrived at the same fundamental idea. The surface belongs to whoever can take it, and the only territory that cannot be taken by force is the territory nobody can see. But fear is only one reason to pick up a chisel, and it is not even the most productive one,

because there is a completely different set of underground works out there, built by people who are not hiding from anything at all. They were not afraid, they were not persecuted, and they were not running. They went down because the ground was better at certain jobs than the surface will ever be, and once you understand what those jobs are, you start to notice that the ground has been quietly outperforming us for two and a half thousand years. For that we go to Italy, and we go into a hill that is basically a factory. Orvieto sits in Umbria on top of a flat-topped block of volcanic rock that rises out of the valley floor with sheer vertical cliffs on every side.

from below it looks less like a town and more like somebody put a small city on a pedestal and dared the neighbours to try something. It is the same broad family of rock we have already dealt with in Anatolia, soft enough to work and stable enough to trust, and the people living up there figured out its properties a very long time ago. Etruscans were carving into this plateau well over two and a half thousand years ago, and the carving never really stopped. The result is a plateau that has been comprehensively hollowed out. Somewhere north of 1,200 separate cavities have been mapped inside it. Tunnels, galleries, wells, cisterns, staircases, quarry chambers, storerooms and cellars,

layered on top of each other across dozens of centuries, connecting, crossing, and occasionally breaking into one another by accident. There is no master plan. There was never a committee. What happened instead is that for 2,500 years, every generation living in Orvieto looked at the ground under their house and thought, I could probably use that, and then simply started digging, which over enough time produces a city with a second, chaotic, inverted version of itself directly underneath. And here is what

makes this stop different from everything we have looked at so far. Nobody in Orvieta was hiding. These people were not sneaking down a hole while an army passed overhead. They were on top of a cliff that made a direct assault a genuinely unattractive career choice. They had walls, and they had a perfectly good town in daylight. They went to the same. Underground because the underground is better at certain jobs. This is not a refuge. This is industrial real estate. Start with the single most important property, which is temperature. Deep inside a rock mass, the surface weather stops mattering. The seasonal swings never penetrate, and you end up with a space that sits at roughly 15 degrees Celsius all year round, without effort,

without fuel, forever. Summer heat wave up top, still 15 degrees. Freezing night in January, still 15 degrees. For most of history, that was the closest thing to climate control available anywhere on earth, and it was free. Now ask an Umbrian what they would like to do with a permanently cool, permanently stable, permanently dark room. The answer, unsurprisingly, involves olives. Olive oil is a diva. Store it warm and it turns rancid. Store it cold and it clouds and congeals, expose it to light and it degrades. It wants exactly one narrow band of conditions and it wants them constantly. The interior of the Orvieto plateau delivers that ban by default, which is why the hill is riddled with underground oil mills. The presses, the settling basins, the storage jars,

the entire production line, all of it moved below the surface, not as a quaint tradition, but as a straightforwardly correct engineering decision. Anyone pressing oil in a shed on the surface was producing an inferior product and losing stock to the weather. Anyone pressing in the rock was not. Which leads to my favourite piece of logistics in this entire episode, and it is a slightly upsetting one. A stone mill needs power, and the power source available at the time was a donkey or a mule walking in circles. The mills, however, were down in the rock, reached by tight staircases and narrow passages that were absolutely not designed with livestock dimensions in mind. So the animals were lowered in, on ropes through shafts, a working mule, entirely against its own preferences,

winched into a cave to begin employment. And in many cases that was a one-way trip. The animal went down, and the animal stayed down, spending its working life walking a circular path in a lamplit chamber, turning a stone in a room with a fixed mild temperature and no weather and no view. This was not cruelty for its own sake. It was the brutal arithmetic of a world with no motors, and the animals were valuable and generally well-fed because a dead mule is an expensive mistake. But it does mean that the Golden Umbrian countryside, the olive groves, the light, the entire postcard, was being converted into liquid gold by an animal that had not seen any of it in years. Not exactly the romantic Tuscan farmhouse fantasy the marketing

department would like you to imagine. Then there are the columbaria, and I would argue these are the cleverest thing in the hill, carved into the outer sections of the plateau, right up against the cliff face, a chambers with walls covered floor to ceiling in small rectangle. niches, hundreds of them per room, arranged in tight grids. It looks like a filing cabinet designed by someone with a grudge. Each niche is a pigeon nest. Each chamber is a dovecote, and the room does not open into the town at all. It opens outward, through narrow, slanted shafts that pierce the cliff face and let daylight and birds in from the open air above a hundred-foot drop. The geometry of those openings is the whole trick. They are sized and angled so that a pigeon can

come and go without difficulty. While anything larger, in particular a hawk or any other predator with an interest in a room full of defenceless birds, simply cannot get through the aperture and cannot approach from the vertical cliff below. The birds fly out over the valley, feed themselves entirely at their own expense on somebody else's fields, and come home to roost in a fortified stone apartment block, because that is what pigeons do, and pigeons are magnificently predictable. The city therefore had a protein supply that fed itself, housed itself, restocked itself by breeding, and required no land, no grazing, no fodder and no attention. During a siege, when every field around the plateau was in enemy hands and every grain store was being counted out in painful

spoonfuls, the pigeons kept flying out, kept eating the besieging army's countryside and kept coming back. The enemy was, without ever knowing it, catering for the defence. Local cuisine still features pigeon prominently to this day, which is one of those cases where a regional speciality is really just a military engineering decision that outlived the war. Underneath all of the industry sits the oldest layer, and it is the one that actually keeps the town from falling apart. The Etruscans, who are world-class hydraulic engineers, and remain criminally underrated compared to the Romans who inherited their tricks, cut networks of drainage tunnels through the plateau known as Kunikuli. These are not passages for people. They are plumbing, driven through the rock at a

carefully calculated shallow gradient, designed to intercept water percolating down through the mass and carry it out through the cliff face before it can do damage. That gradient is the entire point, and getting it wrong ruins everything. Too steep and the flow scours the tunnel and undermines its own floor. Too shallow and the water stands saturates the surrounding rock and softens it. The correct answer is a gentle, consistent, precisely maintained fall over a long distance, surveyed by people working underground, in the dark, without instruments any modern engineer would consider usable, in a tunnel where you cannot see the far end and cannot go back and start again. They got it right, and the proof is not in a museum. The proof is that Orvieto is still up there,

A plateau of porous volcanic rock sitting on softer clay with vertical cliffs on all sides and a town on top is a landslide looking for an excuse. And the only thing standing between the excuse and the outcome is that water gets removed from inside the block before it can build up pressure. Those ancient drains are still part of how the plateau survives, still functioning after more than two millennia, which is a warranty period no contractor alive would agree to in writing. Two and five Canadians will hear the words, cancer. That's why every step and dollar raised matters. On September 19th, join thousands in Toronto for the

Princess Margaret Cancer Foundation Walk. Challenge yourself, friends, and family to walk 21 kilometers in support of life-saving research. Together, we can carry the fire and help create a world free from the fear of cancer. Register today at pmcf walk.ca.ca.ca. At Volvo, safety is not a feature. It's our purpose. rigorous crash testing, decades of learning from real accidents, innovations that help prevent accidents before they happen, and help protect you when they occur. Going above and beyond industry standards, a vision of zero collisions.

Volvo's legacy revolves around you, because safety is about helping to keep you and everyone around you safe for life. Learn more at balvocars.ca.ca slash safety. The digging carried on well past the Etruscans, obviously. Medieval Orvieto put ceramic workshops down there, along with wells and cisterns for every significant house, because a private water supply is the difference between holding out and negotiating. The most famous single piece of engineering on the plateau came in the 1500s, when a pope arrived in a hurry after Rome was sacked and became extremely interested in whether the town he was hiding in could survive being cut off.

The answer involved a spectacular well shaft over 50 metres deep, built with two separate spiral ramps wound around each other, so that mule trains carrying water up never met mule trains going down. A one-way system, in a hole, in the 1500s. The traffic engineering profession likes to think it invented that concept about 400 years later, and the story does not stop in the Renaissance either, because when the Second World War arrived and the sky became the dangerous direction rather than the ground,

the people of Orvieto went into the same tunnels their ancestors had cut for oil and pigeons, and use them as air raid shelters. Same holes, completely different emergency, two and a half thousand years of continuous usefulness out of an infrastructure investment made by a civilisation that has been extinct since before the Roman Empire got going. That is the thing to take away from this hill. Everything we have looked at up to now was built by people running from something specific and their underground spaces were an answer to a threat. Orvieto is what happens when a community stops treating the ground as an emergency.

exit, and starts treating it as a piece of equipment with known specifications. Stable temperature, protection from weather, natural drainage, secure storage, and a cliff face you can use as infrastructure. The Etruscans and everyone after them read those specifications correctly, and built a permanent industrial economy inside a rock, and the entire thing ran on physics that cost nothing to operate. But Orvieto had one enormous advantage that it never had to think about, and that advantage was water. A wet Italian plateau with a water table, springs, rainfall and porous rock that had to be actively drained because there was too much moisture in it. That is a luxury problem. Now take the exact same ambition, the same idea of a

working underground settlement, and move it somewhere with the opposite situation. No rain worth mentioning. No river. Surface temperatures that can cook you. A landscape where the limiting factor is not how much rock you can cut, but whether the air down there is breathable and whether the water arrives at all, that is central Iran, and the solution they came up with is arguably the most elegant piece of environmental engineering in this entire story. The town is Nooshabad, sitting in the desert just north of Kashan, in a landscape that can push past 40 degrees in summer and then flip to freezing at night, because deserts have no interest in moderation. The name itself is a piece of local folklore. The story goes that a sassanid king passing through stopped to drink from a well

here found the water astonishingly cold and clean in the middle of all that heat and named the place after it. So the town is essentially called delicious cold water, which makes it the oldest surviving customer review in Iran. Underneath it is a three-level complex known as Uy, running from around four metres down to about 18, and it was found in the most predictable way imaginable. Sometime in the 2000s a resident was digging in his own yard, working on a well, and broke through into a passage that should not have been there. Two accidental discoveries in this episode now have started with a man doing basic household maintenance, which suggests that the real archaeological tool of the modern era is not ground-penetrating radar. It is a homeowner with a shovel and a

project. The dating puts the original excavation in the Sassanid period, roughly 1500 years ago, and like every good underground site it kept getting used, extended and re-entered across later centuries, right up into relatively modern times. Its purpose was refuge, and the threats varied by era, from raiders sweeping the trade routes to the periodic large-scale unpleasantness that comes with living on the road network between empires. On the surface, that makes it a cousin of what we saw in Capadocia. In practice, it is a completely different machine, because the desert changes the problem entirely. In Anatolia the constraints were rock and defence. Here the constraint is that you are underground in a place with no rain, no river, and air that has to be moved through

a sealed rock volume in a climate that is actively hostile. Stone you can cut, you cannot cut oxygen. So the first thing to understand about Uyi is that it was never a standalone hole. It is plugged into the single greatest piece of infrastructure the Iranian plateau ever produced, which is the Kanat system. A canat is an underground aqueduct and the concept is beautifully simple and monstrously difficult to execute. You find the water table where it sits high, usually in the gravel fan at the base of a mountain,

and then you drive a tunnel from there to your settlement, kilometres away, with a gradient so gentle that the water flows continuously without ever running fast enough to erode the channel it is travelling in. Along the route you sink vertical shafts down to the tunnel at regular intervals for excavation, spoil removal and access. The genius of it is what it prevents. Water in an open channel across a desert evaporates in enormous quantities

and gets contaminated by absolutely everything. Water in a covered tunnel arrives cool, clean and at full volume, driven entirely by gravity, with no pump, no fuel and no moving parts. Persian engineers were running cities on this technology thousands of years ago, and some canats have been delivering water continuously for longer than most countries have existed. It is the most successful infrastructure project in human history that nobody outside the region ever talks about. Ui taps directly into that network, which solves the water question in a single stroke. The refuge does not need to store enough water for a siege, because water is

already flowing past it underground, cool and constant, arriving from a mountain that the enemy standing on the surface cannot even see. That is a fundamentally better answer than a well, because a well is a stock and a canet is a supply. Then comes the air, and this is where the design gets properly clever. The three levels are stitched together by vertical shafts that connect chambers to each other and to the surface, and the whole assembly is arranged to work as a single circuit rather than a set of isolated rooms. Because the deep rock stays at that stable, moderate temperature we already established. While the desert's surface swings violently between roasting and freezing, there is almost always a substantial temperature difference between inside

and outside. That difference is a pump. Warm air rises out of one shaft, cool air is drawn in through another, and the system breathes on its own, all day, all night, driven by nothing but the fact that the desert cannot make up its mind. The same country invented wind catchers on the surface for exactly the same reason, and Uye is essentially that principle turned inside out and buried. The result is a refuge where a large group of people can sit for an extended period without the atmosphere going stale, which sounds unglomerous right up until you consider the alternative. Beautiful carving is optional, breathing is not. The defensive design deserves a mention too, because it takes an idea we have already seen and executes it in a completely different key.

As at Derinkou-Yu, the corridors do the fighting, deliberately narrowed, so that anybody moving through goes one at a time and bent forward. But there are no half-ton rolling doors here. The Nushabad approach is subtler and frankly, meaner. The passages change height and width unpredictably. The levels connect through openings positioned so that an intruder emerges awkwardly, off balance, and in the wrong posture, into a space where somebody who knows the layout is already waiting. Carved into the walls are shallow niches at seat height, so that guards could sit in position for hours in total darkness, and smaller niches for oil lamps, position to light what needed lighting and leave the rest black. Think about what that means in practice. An attacker with

a torch coming down a passage as a glowing target announcing his own arrival and destroying his own night vision. A defender sitting in a dark alcove is a wall until he decides otherwise. The complex is not built to withstand an assault. It is built so that an assault is never a fair contest for a single second, which is a considerably more efficient use of everyone's time, which makes Nushabad the perfect counterpoint to the giant we looked at in Kappadocia. Two societies with the same basic requirement, hide a population and keep it alive, working in completely different rock and completely different climates, and neither one copying the other. One answered with vertical depth, massive stone plugs and a protected well.

The other answered with a plumbed in mountain water supply, a self-ventilating shaft network and corridors designed to humiliate anyone who entered them. Same question, different geology, different answer, both correct. Now let us take that same instinct, the idea of building down as deliberate infrastructure, and hand it to a civilization with a much bigger budget and a taste for showing off, because everything we have seen so far has been functional, impressive, ingenious, occasionally elegant but fundamentally utilitarian. What happens when a kingdom decides that a piece of underground water infrastructure should also be one of the most beautiful buildings anyone has ever constructed. You get northern Gujarat, and you get a structure that is best described as an

upside-down skyscraper. Raniki Vav sits at Patan, and it is a step-well, which is a building-type Western architecture never developed and honestly never recovered from missing. The principle behind a step-well is a response to the monsoon. In this part of the world, the water table does not sit politely at one level. It rises dramatically during the rains and then sinks through the dry months, sometimes by a considerable distance. A conventional well with a bucket handles that badly, so the solution is to build a staircase down to the water and keep going. So that whatever level the water has fallen to that month, you simply walk down the appropriate number of steps, and there it is. The building tracks the season by being taller than the problem.

Rani Kivav takes that utility and escalates absurdly. It runs roughly 64 metres long, around 20 wide, and about 27 metres deep, arranged over seven descending levels. It was commissioned in the 11th century by a queen, Udai Amati, as a memorial to her late husband, King Beamer I. Which is worth pausing on, because as a gesture of remembrance, most cultures land somewhere around a tomb, a statue, or in the modern era a bench with a small plaque. She built a functioning public water source the size of a city block, decorated it like a temple and gave it to the population forever. That is a rather higher bar, and every morning spouse since has been quietly letting the side down.

Structurally, this thing is fighting a battle that above-ground buildings never have to think about. A normal building deals with its own weight pressing down. A stepwell deals with the entire surrounding landscape pressing in. Soil under pressure behaves like a slow liquid, and it wants to close a hole this size the way water wants to fill a glass. The deeper you go, the harder it pushes, and it pushes sideways. The answer is visible in the shape of the thing. The stepped corridor descends between tiers of pillared pavilions,

story upon story, and those pavilions are not decoration, and they are not viewing platforms. They are the bracing. Each level of columns and beams ties the two long walls to each other and to the mass of the structure, converting inward pressure into compression carried across the whole assembly rather than a bending load on a freestanding wall.

and critically the proportions get heavier as you descend. The upper pavilions are relatively light and open. The lower ones are thicker, more closely spaced, more massive, because that is where the pressure is worst. The entire building is a gradient of strength matched to a gradient of load, designed by people with no formal soil mechanics, and a very clear understanding of what happens if you get it wrong. And then, having solved a serious geotechnical problem,

they covered the solution in more than 500 major sculptures, and something on the order of a thousand smaller ones. Deities, avatars of Vishnu, celestial dancers, serpent maidens, guardians, and an entire population of figures arranged across every available surface of every level, all in sandstone, all carved to a standard that would be extraordinary in a temple built on flat ground in comfortable conditions. Here is the part that raises the difficulty enormously. The figures were largely carved on individual blocks and then assembled in place. down in the pit as the structure went up from the bottom. That means every block was simultaneously a piece of art and a piece of load-bearing masonry, and it had to fit its neighbours exactly, because a poorly

fitted block in a wall holding back several thousand tonnes of wet soil is not a cosmetic issue. Naturally, there was also no adjusting a figure after the fact. You cannot add stone back onto a sandstone carving, and you cannot ask the sculptor for a slightly wider version of the one he finished last month. This was a giant three-dimensional puzzle with no spare pieces, assembled at the bottom of a hole on a schedule set by the arrival of the monsoon, and then, in the greatest plot twist in the history of building preservation, the river ruined everything and thereby saved it. The Saraswati, the river this whole region depended on, shifted its course and flooded. Silk poured into the stepwell and kept pouring, until the entire structure, all seven levels of it,

was packed solid with mud and sediment. From a functional point of view, that was the end. The Queen's Monument was gone, buried under a wet grey plug, and it stayed that way for something like seven centuries while the memory of it faded to a rumour and a name. Except that silt, it turns out, is an outstanding conservator. Sealed under compacted mud, the sandstone was cut off from rain, from wind, from temperature cycling, from sunlight,

from acidic weathering, and just as importantly, from people. No iconoclasm, no vandalism, no souvenir hunting, no well-meaning restoration in the wrong stone, no 400 years of visitors touching the same figure's foot until it dissolved into a lump. The carving simply stopped experiencing time. When systematic excavation finally cleared it out in the 20th century, what emerged was not the eroded ghost you would expect from an 11th century structure. It was crisp. faces, fingers, jewellery, folds of fabric, the details that are always the first thing to disappear from ancient stonework, still there, still sharp, because the disaster that destroyed

the building's usefulness had accidentally packed it in protective wrapping. The site is now a World Heritage listing and appears on Indian currency, which is a decent career recovery for something that spent 700 years as a mud pit. So the second motive closes with a clear conclusion. The ground is not only a place to hide in. Handled properly, it is a machine that holds temperature, moves air, transports water, resist weather, and stores things better than anything humans could build on the surface. And the civilisations that understood this were not retreating from the world, they were exploiting a resource that happened to be underneath it. But there is one more reason people have gone into the rock, and it is the one that makes the least practical sense

and produce the most staggering results. Because you do not need a hundred sculptures and a perfect aligned shaft of sunlight to hold water or store oil. The next set of builders were not solving a problem at all. They were trying to reach something, and they decided the way to reach up was to cut down. Western Kazakhstan, the Mangistau region, a slab of land wedged between the Caspian Sea and several hundred kilometres of nothing in particular. This is one of the emptiest inhabited landscapes on the planet, a chalky limestone plateau cut apart by canyons, dry valleys and eroded ridges that look less like scenery, and more like the leftover packaging from a much larger geological project. The colours are white, pale yellow and rust. There are no trees to speak of.

The wind does not stop. Summer bakes, winter freezes, and the whole place gives off the strong impression that it would prefer you left. Two and five Canadians will hear the words, you have cancer. That's why every step and dollar raised matters. On September 19th, Thousands in Toronto for the Princess Margaret Cancer Foundation Walk. Challenge yourself, friends, and family to walk 21 kilometers in support of life-saving research. Together, we can carry the fire and help create a world free from the fear of cancer. Register today at pmcf walk.ca. Hey, y'all, it's Kelly Clarkson with Wayfair.

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And yet for centuries this was not an empty corner at all, because the caravan routes ran through it. Traffic moving between Central Asia, the Caspian and the lands beyond had to cross this plateau, and where there is traffic there are stopping points, and where there are stopping points there are people with something to say to travelers. The people in question were Sufi mystics, and what they left behind are mosques carved directly into the rock.

Now, a nomadic society is not supposed to produce permanent architecture. That is essentially the definition. If your entire economy runs on moving herds across enormous distances, your building tradition is portable, brilliant and made of felt, and constructing anything you cannot pack onto a camel is a category error, which makes the underground mosques of Mangistow genuinely strange. Here is a culture that deliberately does not build, producing structures that cannot be moved,

cannot be dismantled and cannot be replaced, cut by hand into a cliff, in a region where the nearest anything is a very long ride away. The oldest of them, associated with a dervish remembered as Chopinata, goes back around a thousand years and belongs to the wave of Sufi teaching that spread through the step along the trade routes rather than by conquest. The mosque is cut into a low limestone outcrop with an entrance that hardly announces itself at all, opening into a series of chambers, cells and niches worked out of the rock. It is not a display building. It reads as a place designed to be found by people who already knew it was there, which is the general

architectural mood of the whole region. The one that gets the most attention, and deserves it, is Shackback Atta. It is cut into the face of a limestone cliff on the tube-carragon side of the peninsula, and the interior is where things stop being a cave and start being architecture with opinions. The floor plan is a cross, four arms extending from a central space, with columns left standing in solid rock at the corners, arches worked into the walls and carved decoration across the surfaces, including inscriptions and figures of horses and open handprints. That cruciform layout is unusual, because it is not the standard geometry of a mosque, and it points at something interesting about where this region sits on the map. Mangistau was a crossroads long before Islam arrived.

Zoroastrian practice ran through this part of the world for centuries. Christian communities moved along the same trade corridors, and when a new faith arrives in a place with deep existing traditions, what usually happens is not deletion, but absorption, so the builders worked with a spatial vocabulary they had inherited and filled it with a new meaning. The building is a conversation between several centuries of belief, conducted in stone,

and the participants were not consulted about being placed in the, same room. Then there is the light, and this is the part I find genuinely remarkable. Cut vertically through the rock above the interior are shafts that bring daylight down into the chamber. In a building with almost no windows deep inside a cliff, those shafts are the entire lighting system, and the effect is dramatic on any ordinary day, a hard column of daylight dropping through cool, dim air onto a stone floor while everything around it stays in shadow. That alone would justify the work, but the shafts were not simply punched through wherever the rock was easiest. They were positioned so that the beam moves across the interior through the year

and on the days around the equinoxes falls directly onto the Mirab, the niche marking the direction of prayer, which turns the mountain into an instrument. The building is not just a mosque, it is a calendar, and it delivers exactly two notifications a year, with perfect reliability, requiring no maintenance, no batteries and no subscription. Consider what that took to achieve. You're standing on the top of a cliff with a pick, and you need to drill a shaft down through many metres of solid limestone to arrive at a specific point in a chamber you cannot see,

at a specific angle, calculated to intercept the position of the sun on a specific pair of dates. You cannot check your work halfway. You cannot correct the angle once you have started, because a shaft cut through stone is a commitment, and the only tool available for fixing a badly aimed one is a second shaft and a great deal of embarrassing. That requires solar observation carried out over years, a working knowledge of how the sun's path

shifts through the seasons at this exact latitude and the confidence to translate that knowledge into an irreversible hole. For a community without permanent settlements, tracking the year like that is not an academic exercise, knowing precisely when the seasons pivot is the difference between moving the herds at the right moment and moving them at the wrong one and the wrong one cost animals. So the mosque is doing double duty. It is a spiritual anchor and a timekeeping device, and the same shaft of light serves the man who wants to pray correctly, and the man who needs to know whether it is safe to head for the summer pastures. Multi-purpose design, roughly 900 years before anyone thought to make it a selling point. The surroundings complete the picture,

because none of these sites stands alone. Around the entrances spread necropolises, and they are enormous. Thousands of grave markers cover the ground in dense fields that run right up to the cliffs, and they are not simple headstones. There are tall carved pillars, some of them elaborately worked with patterns and inscriptions. There are stones cut into the shape of rams, which for a herding culture is not a decorative flourish. It is the direct symbolic language of wealth, life and survival. There are small stone structures over family plots, and markers designed with distinct forms for men and for women. Different shapes, different symbols, different messages, an entire visual grammar for the dead maintained across centuries by people whose houses were made of felt and wooden

frames. And this is where Mangistow makes a point that separates it from everything else we have looked at. The underground works we have covered so far were about the living. Concealment, water, storage, temperature, defence, all of it aimed at getting a population through a bad situation and back up into daylight. Here the relationship inverts. Nobody is hiding. Nobody is being besieged and nothing is being stored. These sites exist to attach a mobile society to a fixed point in the ground and the graves are the mechanism. A nomadic people covering thousands of kilometres in a lifetime still needs somewhere permanent and the permanent thing is not a house or a capital city. It is where the ancestors are. The result is a form of geography that a settled society tends to get

completely backwards. We tend to assume the important places are where people live, and the graveyard is a support function on the edge of town. In Mangostow, the pattern runs the other way. The fixed point is the burial ground and the rock-cut mosque beside it, and the living orbit that point, returning across long distances at intervals, and the tents and herds move around it like weather around a mountain. The practice held for an extraordinarily long time. Later teachers continued the tradition well past the medieval period, with further underground complexes carved in later centuries, and pilgrims still travel out across that plateau today to visit them, in numbers that would astonish anyone who has looked at the region on a map and concluded that nothing happens there.

It is a serious journey even now, on modern roads, in a vehicle with air conditioning, and the last stretch to some of the sites involves walking. Historically, the journey was the point. A shrine that is easy to reach asks nothing of you. A shrine that is easy to reach asks nothing of you. A shrine. at the end of several days across a waterless plateau extracts something, and that cost is precisely what made the arrival mean anything. There is one more thing worth noticing about the technical side. The limestone here is workable, but the region gives you nothing else. No timber for scaffolding or beams, no fired brick without fuel, no quarried stone transport network, no local supply of anything. If you want a building on this plateau, the material has to already be present, which leaves you

exactly one option. Use the cliff and remove what you do not want. The mosques of Mangistau are not underground because someone preferred the aesthetic. They are underground because subtraction was the only construction method the landscape would permit, and the builders turn that limitation into a form of architecture, with light shafts, cruciform halls and carved columns holding up nothing at all. Which brings us to the obvious escalation. A carved mosque in a cliff is one thing. It is set into the rock, borrows the hillside as three of its walls, and it lets the mountain do most of the work. But what if you did not want a building set into a hill? What if you wanted a freestanding structure with four proper walls, a roof, windows, columns, and a full interior, and your

material was still a single solid mass of stone with no blocks, no mortar, and no possibility of assembling anything? What if you decided that the building should not lean on the rock at all, but stands separate from it, carved out as one continuous piece, with a trench cut all the way around it to prove the point. That is Ethiopia, and it is the most audacious construction project in this entire episode. The northern Ethiopian highlands, roughly two and a half thousand meters up, in a landscape of steep ridges and thin cold air where the sun is fierce and the rainy season arrives with genuine violence.

The town is Lalebella, and it is home to 11 churches that break the rules of construction so thoroughly that people looking at them for the first time usually assume they are seeing something excavated, like a ruin uncovered by archaeologists. They are not. Nothing here was buried and nothing was dug up. Every one of these buildings was made by deliberately removing the landscape from around a shape that a human being had already decided on. The context matters, because this was not a slow accumulation of work across generations the way most of our previous stops were. This was a project, with a deadline and a political motive. In the late 12th century, Jerusalem changed hands,

and access for Christian pilgrims from this part of the world became difficult, expensive and dangerous. Ethiopian Christianity is ancient, older than most European versions of it, and the pilgrimage to the holy city was central to religious life. Suddenly the destination was effectively out of reach. So the ruling king of the Zagui dynasty, remembered ever since by the name of this town, took the most audacious possible approach to the problem. If the faithful cannot travel to the holy city, build the holy city here.

Not a copy, not a shrine with a plaque, but a functioning sacred landscape with its own topography, its own named sites, and its own river, laid out so that a pilgrim could walk the route without leaving the highlands, rebranding at a scale that no marketing department has matched since. Now the technique? Because this is the part that deserves your full attention. Everything humans normally build is additive. You gather material, you place it, you stack it, you join it.

Even in the carved sites we've already visited, the builders were working into a hillside, letting the mountain provide the exterior and hollowing out the inside. Lalibela does something else entirely. These churches are freestanding buildings with four external walls, roofs, windows, doorframes, and decorated facades, sitting in open pits, and every one of them is a single wall. single continuous piece of rock still attached to the bedrock at the base. There are no blocks, there are no joints, there is no mortar anywhere in the structure because there is nothing to join.

The sequence goes like this. First, the masons marked out a rectangle on the surface of the red volcanic rock and cut a deep trench all the way around it, isolating a solid block from the surrounding stone on all four sides, sometimes to a depth of over ten metres. At the end of that stage they had produced at enormous cost in labour, a large rectangular lump of rock in a hole and nothing else. That is the point in the project where every modern client would be asking hard questions.

Then the work turned inward and downward. Starting from the top surface, which would become the roof, the masons cut down into the block, opening the interior, shaping the nave, leaving columns standing where columns were needed, carving arches and vaults into the ceiling as they descended, and hollowing the whole thing out into a functioning church from the inside. They worked from the roof down, which is exactly backwards from the way any structure has ever been built, and it has one gorgeous side effect. There is no scaffolding, ever. You're always standing on the

material you have not removed yet, and the floor descends with you as the work progresses. The building site provides its own platform and then deletes it. But that reversal creates a nightmare, and the nightmare is that subtractive building has no revisions. Every decision is permanent from the first strike. A column that is too thin is not a redesign. It is a structural failure with no remedy. A ceiling cut 15 centimetres too low is 15 centimetres that no longer exist anywhere in the universe. You cannot bring in more rock. You cannot patch a mistake with a block, and you cannot move a wall outward because outward is now air, which means the entire finished building with all of its proportions, its column spacing, its window placements and its interior geometry had to exist

completely in somebody's head before the first tool touched the surface, and then be executed accurately by a large workforce cutting blind through solid stone with no way to check the plan against the result until it was too late to change anything. And the scale is not modest. The largest of them, Bet Medina L'em, is generally described as the biggest monolithic rockhune church in the world, over 30 metres long, more than 20 wide, around 11 metres tall, ringed by a colonnade of rectangular pillars carved directly out of the parent rock. It is the size of a serious cathedral, and it was produced by removing several thousand cubic metres of stone by hand, chip by chip, and carrying every fragment of it out of the hole.

The most famous is Beat Giorgis, standing alone in its own deep square pit, carved in the shape of a cross when seen from above. Three tiers of stepped cross-form roof, clean vertical walls, sitting in a shaft cut down into the rock with the surrounding ground level at roof height. To reach it, you walk down a trench, an approach from below, which means the building reveals itself from the top first, and then rises above you as you descend, which is not an accident. Every other church you have ever entered was designed to be approached from the front.

This one was designed to be approached from the sky. The local tradition holds that the work was carried out with angelic assistance, with the human masons cutting by day and angels continuing through the night, which is the kind of story that tends to attach itself to any project where the labour totals look implausible. Modern estimates for the workforce and time required are debated, and the honest answer is that we do not know exactly how it was organised. What we do know is that these are the products of a highly skilled tradition

that clearly did not start here, because nobody carves at this level on their first attempt. Now, the part that turns a collection of remarkable churches into an actual designed complex, the buildings are connected by a network of trenches, passages and tunnels cut through the rock between them, and those channels are doing at least three jobs simultaneously. They are circulation, allowing priests and pilgrims to move between the churches at a level below the surrounding ground. Two and five Canadians will hear the words, you have cancer. That's why every step and dollar raised matters.

On September 19th, join thousands in Toronto for the Princess Margaret Cancer Foundation Walk. Challenge yourself, friends, and family to walk 21 kilometers in support of life-saving research. Together, we can carry the fire and help create a world free from the fear of cancer. Register today at pmcf walk.ca. Hey, y'all, it's Kelly Clarkson with Wayfair. Ever order furniture online and wonder, what if? Like, what if it doesn't hold up? That sofa was four days old.

You should have ordered from Wayfair. With Wayfair, there's no what-if. Just style you love and quality you can trust. Visit Wayfair.ca. Wayfair, every style, every home. They are ceremonial because a route that takes you through a dark tunnel and then out into daylight in front of a façade is a route that has been choreographed rather than merely built,

and most importantly, they are drainage. That last function is what keeps the entire site alive. The Ethiopian Highlands gets serious rain, and here is the fundamental problem with carving builds. into pits. A pit is a bucket. Every trench, every courtyard and every sunken church is a hole in the ground with vertical sides, and during the rainy season the water has nowhere to go except into those holes, where it will pool against the foundations of a soft volcanic rock building and quietly destroy it from below. Water sitting against carved stone is the single most effective demolition

method in existence. It just works slowly enough that nobody blames the architect. So the trench system is graded and connected to carry runoff away, moving water between the courtyards and out of the complex rather than allowing it to collect. The passages that look purely symbolic are functioning as storm drains, and the entire site is a hydraulic system disguised as a pilgrimage route. The centrepiece of that arrangement is the channel that separates the northern group of churches from the southern group, named after the River Jordan. Symbolically it completes the map because a new holy city requires the geography of the original,

and a pilgrim crossing it is repeating a crossing with 2,000 years of meaning attached. Practically, it is the main drain. The most sacred watercourse on the site is also the one keeping the foundations dry, and the fact that those two roles coincide is not a compromise, it is the whole design philosophy. In this complex, symbolism was not decoration applied to a working structure. Symbolism and function were specified together and then cut into the rock as one continuous idea,

which leads to something that separates Lalibela from nearly everything else in this episode. These are not archaeological sites. They are not preserved, interpreted, roped off or reconstructed for visitors. They are working churches, in continuous use since they were made, staffed by priests, filled with services, hosting festivals that draw enormous crowds of pilgrims from across the country. Wooden crosses and illuminated manuscripts kept inside them are not exhibits, they are equipment. Nobody rediscovered Lalebella, because nobody ever stopped going. In an episode largely about things that were forgotten and then stumbled upon by accident,

this is the one that simply never closed. That continuity does come with a modern cost. Soft volcanic rock exposed to eight centuries of highland weather erodes, and several of the churches have needed protective shelters built over them, which are large, functional and aesthetically about as sympathetic as a temporary car park roof over a masterpiece. conservation work is ongoing and complicated because you cannot simply replace a damaged element on a building that has no elements. Repairing a monolith means repairing the mountain it is part of, which is a category of engineering problem most restoration teams never have to face.

Step back and look at what this actually represents. Everything we have covered so far treated the ground as a resource to be used or a place to escape into. Here the ground is the raw material of an idea. A king decided that a sacred city should exist in a place where it did not, and the only way to make it exist was to take an ordinary section of Highland Rock and remove everything that was not a holy city. The mountain did not gain a building. The mountain lost everything except the building. That is the purest expression of the principle we started with. Above ground, you construct by adding, down here, you construct by deciding what to take away, and the finished thing is defined entirely by what you chose to leave behind. Which raises one final question for this section. Every builder we have

looked at has been working with rock that stays where it is put. Chalk, tough, limestone, sandstone. They erode, they crack, they get damp, but they are fundamentally passive materials that hold their shape and weight. So what happens if you try to carve a cathedral out of a rock that moves? A material that behaves, over long enough timescales, less like stone and more like something slowly flowing, actively trying to close any space you open inside it. For that, we go to Columbia, and 200 metres down into a mountain of salt. Fifty kilometres or so north of Bogota in the Colombian Andes sits the town of Zippaquira, and underneath it is a mountain that used to be an ocean. A very long time ago this was a shallow sea, and when the water evaporated it left behind

an enormous deposit of rock salt. Then the Andes happened, the whole region was shoved upward by tectonics, and the result is a mountain with a body of solid halite inside it, sitting there at altitude hundreds of kilometres from the nearest coast, in one of the wettest countries on the continent. Long before any European arrived, the Muska people were mining it. They had been extracting salt here for centuries, and they understood exactly what they were sitting on, because in a world without refrigeration,

salt is not a seasoning. It is the technology that lets you keep meat, preserve fish, feed a population through a bad season, and trade with people who cannot get any. The whisker turned it into a currency, moulding salt into standardised cakes and using them as a medium of exchange across a trading network that ran for hundreds of kilometres.

So while other civilisations were fighting over gold, this one was running an economy on the thing you keep next to the pepper, and honestly they had the better product because you cannot eat a gold coin, and gold has never stopped a single ham from going bad. When the Spanish arrived, they took over the operation because of course they did, and extraction expanded over the following centuries into a proper industrial mine,

with galleries and shafts driven deep into the salt body. And that is where the interesting part of this story starts, because the thing that eventually got built down there was not commissioned by a king, a bishop or a government. It was built by the workforce. Salt mining before modern safety regulation was a job with a genuinely alarming risk profile. You are deep inside a mountain, in the dark, with several hundred metres of rock overhead,

doing heavy physical labour in a place where a bad day is not an inconvenience, it is a funeral. So the miners did what people in dangerous trades have always done, which is get religious specifically on the way to work. They cut small niches into the walls of the working galleries, placed figures of saints in them, and stopped to pray before starting a shift. That was not architecture. It was a shrine the size of a kitchen cupboard, carved by a man on his own time with the tools already in his hands. But there were a lot of the last. of them, over a lot of years, and gradually the mind took on the character of a place where people worshipped as a matter of routine. What exists now is the formal, monumental, professionally engineered

descendant of those cupboard shrines, which makes it one of the very few enormous religious buildings on earth that grew upward through the social structure rather than downward from it. Normally the person who orders a cathedral has a title, a treasury and a portrait commissioned for the occasion. Here the original clients were men in boots trying to improve their odds. The first full-scale church inside the mine was completed in the middle of the 20th century, and it was a hit immediately, drawing pilgrims and visitors in numbers nobody had planned for. It also had a problem, which we will come back to, and by the early 1990s the structural concerns was serious enough that it was shut down. The replacement, opened in the mid-1990s,

was built deeper still, roughly 60 metres below the original, and that is the one people visit today, a complex of chambers, chapels and processional spaces around 200 metres underground, with a main space capable of holding thousands of people at once. The route intakes you first past a sequence of small chapels, marking the 14 stations of the cross, each one carved as its own chamber, with its own cross and its own lighting, so that arriving at the main space is a walk rather than a doorway. Then the ceiling opens out and you get the central nave, with a vast cross cut in relief into the rock face at the far end, lit from below so that it appears to hang in the air rather than sit on the wall. It is genuinely theatrical, and the theatre is doing real work,

because the raw material here is grey, and the lighting is the only thing supplying colour, mood or drama. Now the engineering, and this is where Zippaquira becomes fundamentally different from every other site we have visited. Salt is not a normal rock. Under the pressure of a mountain sitting on top of it, Hallite does not simply hold its shape the way limestone or granite does. It deforms, slowly, continuously and permanently. Geologists call the behaviour creep, and it means that over months and years salt underload flows, in much the same way a glacier flows without ever cracking. This is why salt pushes upward through overlying rock to form domes, and it is why the energy

industry stores oil and gas in salt caverns, because if a fracture opens in the wall, the salt closes it by itself. A self-healing rock sounds delightful right up until you work out what it means for a building. It means the mountain is trying to shut the cathedral. Every chamber cut into that salt body is a void, and a void inside a creeping material under load is a temporary condition by definition.

The rock is pressing inward from every direction, continuously, and left alone for long enough it would squeeze those spaces smaller and smaller until they closed completely. It is the slowest demolition crew ever assembled, working every hour of every day for free, and it will never get tired, never get bored and never go on strike, which is why the columns down there are enormously thick and the vaults are so broad. Not for grandeur, and not because the designers were feeling nostalgic

about Gothic proportions. Those shapes exist because the only way to hold a space open inside a material that pushes in from all sides is to give the load a path that can travel as pure compression, distributed across curved surfaces and massive pillars, with no thin spans and no sharp internal corners where stress can concentrate. A slender, elegant column in salt is not a design choice. It is a countdown. Every proportion in that building is dictated by the fact that the rock is active and impatient. That is broadly what caught up with the earlier church too. Spend enough decades inside a deforming salt mass without a design fully adapted to the behaviour, and the deformation eventually presents its bill.

The current complex was planned from the outset around that reality, and it is monitored continuously. Instruments track convergence, which is the technical term for the walls, slowly walking toward each other, and engineers watch those numbers the way a doctor watches a patient with a chronic condition. Not an emergency, just something that would definitely become one if everybody stopped looking. So this is a building that requires permanent medical supervision, which is not a phrase anyone applies to a cathedral made of stacked limestone blocks, because limestone has no ambitions. This one does. And then there is the sensory detail that visitors always mention and never expect, which is what happens to sound. Every large

religious interior you have ever stood in was shaped, deliberately or by tradition, around reverberation. Hard flat surfaces, high vaults, and stone floors produce a long echo. And that echo is not a side effect, it is the instrument. Chant works because of it. Organ music was written for it. The overwhelming sense of vastness you feel walking into a cathedral is largely acoustic, delivered by your own footsteps returning to you from a long way off a couple of seconds later. Salt refuses to play. The rough crystalline surfaces of a salt chamber absorb and scatter sound rather than reflecting it, and the effect is startling. The echo simply never arrives. You're standing in a space big enough for a crowd of thousands, under a ceiling far above your head, and your voice goes out and does not come

back. Speech sounds oddly close and flat, like talking in a room full of heavy curtains. Footsteps land and disappear. The silence has a physical density to it that has nothing in common with the ringing emptiness of a stone church, which produces a fascinating outcome. The building achieves the emotional effect religious architecture has always chased, that feeling of being very small inside something very large by doing the precise opposite of what every other tradition does. Instead of amplifying you into a huge space, it absorbs you. The vastness is never announced.

It is implied by the total absence of any response, and if anything, that is more unsettling. A cathedral that echoes is telling you the room is big. A cathedral that does not is telling you the mountain has no interest in your contribution. worth noting for the pedants among us that it is not technically a cathedral in the administrative sense, since it has no bishop of its own, so on paper it is a church that everybody has collectively agreed to call something grander. Nobody is going to win that argument and nobody should attempt it. It also remains an active place of worship with regular services and very large congregations,

alongside a constant flow of visitors who came for the spectacle rather than the sacrament, producing the mildly comic modern situation of a working church, operating as one of the country's biggest tourist attractions, inside an active salt mine, 200 metres below the Andes, and that closes the third motive. What this place demonstrates, as Ethiopia and the Kazakh Plateau did in their own ways, is that going into the rock for religious reasons was never about concealing the practice. Nobody here was hiding. They went down because the rock offered something the surface could not supply at any price, permanence, controllable darkness, silence, and the specific experience of standing inside the planet instead of on top of it. Which brings us to the end of the historical

material, and to a question you may have been quietly assembling for a while now. All of this is ingenious, all of it is impressive, and all of it is also finished. These are heritage sites, conservation projects, places with ticket offices. The ancient world went underground because it had to, and then the modern era arrived. with air conditioning, structural steel, cheap concrete and elevators, and the whole impulse became a historical curiosity, except it did not. Because there is a town in the Australian desert right now where most of the population lives underground on purpose, and there are wealthy cities in the developed world drawing up formal master plans for the space beneath their streets. The reasons have changed

completely. The instinct has not moved an inch. South Australia, roughly in the middle of an area most maps deal with by simply leaving it blank. The town is Cuba Pidi, and it exists for exactly one reason. In 1915 a prospecting party stopped here, and a teenage boy in the group found Opal. Not a little bit of Opal. This region turned out to hold the richest opal deposits on the planet, and the town that grew on top of them still supplies a large share of the world's supply. The problem is the location. Summer temperatures here regularly push past 45 degrees Celsius and can reach into the 50s. There is essentially no rainfall to speak of,

no river, no shade, no trees, and dust storms arrive with enough force to strip paint. The landscape is a flat expanse of ochre-coloured spoil heaps, thousands of them, because a century of mining has left the surroundings looking like the surface of a planet that failed its inspection. There is no grass anywhere. The local golf course is played on dirt,

mostly at night, with balls that glow, and every player carries a small piece of artificial turf around with them to tee off from, which is either the most Australian solution ever devised or simply the only one available. Living on the surface here in the era before refrigerated air conditioning was not merely uncomfortable. It was a serious medical proposition, and the early miners, many of them soldiers returning from the First World War with an intimate and unwanted expertise in digging into the ground, looked at the situation and reached a conclusion that would have been immediately obvious to a

Capadocian farmer, an Umbrian oil presser or a Persian engineer. Go inside the rock. The homes here are called dugouts, and they are not caves in any romantic sense. They are excavated houses, cut horizontally into the low hills and rises around the town with proper doorways, hallways, bedrooms, kitchens, plastered or bare rock walls, tiled floors, wiring, plumbing, and everything else you would expect from a normal house except windows on more than one side. The rock is a soft, stable sandstone that holds a ceiling without any support at all, which means no beams, no columns, no props, nothing. You cut a room, and the room stays a room, and the reason for all of it is a single physical property we have already met several times on this trip. Put enough mass between yourself

and the sky, and the weather stops applying to you. Down in a dugout, the temperature sits at a steady 23 degrees or thereabouts, year-round, day and night, through a 50-degree summer afternoon, and through a cold desert night without a single air conditioner running. Two and five Canadians will hear the words you have cancer. That's why every step and dollar raised matters. On September 19th, join thousands in Toronto for the Princess Margaret Cancer Foundation walk.

Challenge yourself, friends, and family to walk 21 kilometers in support of life-saving research. Together, we can carry the fire and help create a world free from the fear of cancer. Register today at PMCFWalk.CA. Hey y'all, it's Kelly Clarkson with Wayfair. Ever order furniture online and wonder what if? Like, what if it doesn't hold up?

That sofa was four days old. You should have ordered from Wayfair. With Wayfair, there's no what if. Just style you love and quality you can trust. Visit Wayfair.ca. Wayfair, every style, every home. Same principle that kept Umbrian olive oil in perfect condition and the same principle that made a Stepwell staircase

the most pleasant place in Gujarat in May. The physics have not been updated, only the electricity bill has. Which is really the joke of the whole thing. This is not a heritage site and nobody living in one of these houses is preserving an ancient tradition. They are just refusing to pay to cool a building against a desert that will win. Air conditioning in this climate is not simply expensive, it is a permanent tax with no end date, and it fails at the worst possible moment, whereas a hillside continues functioning during a power cut with no complaints and no maintenance schedule.

town has taken the idea considerably further than housing. There are underground churches, including a Serbian Orthodox one with carvings cut directly into the rock walls. There are underground hotels where you can book a room with no window at all and sleep in a silence most city dwellers have never experienced. There are shops, galleries, museums, a bookshop, bars, a meaningful share of the population lives below ground, and the surface of the town is largely infrastructure, industry and parking. There is also a delightful economic quirk built into the arrangement. Adding a room to your house here means hiring a tunneling machine and cutting further into the hill, which is dramatically cheaper than building an extension out of materials that have to be trucked across a continent.

And every so often, someone renovating their living room hits a seam of opal in the wall of their own home and the extension pays for itself several times over. Home improvement as a lottery ticket. Try getting that from a conservatory in the suburbs. Naturally, there are rules. Dugouts need ventilation shafts to the surface, and there are regulations covering how much rock you have to leave overhead and where you can dig. Because in a town built on a mining field, the risk is not that your ceiling collapses. It is that your neighbour tunnels enthusiastically into your bathroom. The council spends a genuinely surprising amount of time on that specific issue. Now, it would be easy to file Cuberpidi under eccentric Outback Curiosity and move on,

but the same logic is being applied right now at enormous expense, by some of the wealthiest and most carefully planned cities on earth, and they are not doing it for the novelty. Take Helsinki. Finland sits on some of the oldest and hardest bedrock in the world, granite that is stable, dry and strong enough to hold enormous spans without support. The Finns looked at that and did something no other city had done. They zoned it. Helsinki has an underground master plan, a formal piece of city planning that treats the bedrock beneath the city, has a mapped, allocated, reserved resource in exactly the same way surface land is treated. Space below ground is designated for specific future purposes so that nobody excavates a car park

in a volume that has been set aside for a water tunnel in 30 years' time. What is already down there is remarkable. Hundreds of facilities, metro lines, road tunnels, parking, a swimming pool complex, data centres, water treatment, shopping levels, and a network of civil defence shelter with capacity for a very large share of the population, most of which spend their ordinary lives being used as car parks, sports halls and storage, dual-purpose infrastructure, running as normal city amenities until the day they are needed for something else. Then there is Montreal, which went underground for the opposite reason to the Australian desert. Winters in Quebec are long,

dark and severe, and moving around a city in that climate is a daily negotiation with the weather. Starting in the early 1960s, developers in the city began linking buildings below street level, connecting to the metro system, and the result grew into a network of tens of kilometers of connected passages tying together malls, offices, hotels, universities, transit stations and apartment towers. Enormous numbers of people use it every day. You can arrive in the city, get to your office, buy lunch, see a film, take the train home and never be outdoors, which in February is not a gimmick, it is the entire point. Heat in one case, cold in the other, and the identical answer.

When the surface becomes hostile, the space beneath it becomes valuable, and that is where this whole journey resolves. Look back at everything we have covered, and the variety is almost comical. French villagers hiding a population under farmland, a stacked 18-level complex in Anatolia, a second city under the floors of a living Turkish town, an Italian plateau converted into a factory, a desert refuge plumbed into a mountain aqua,

a queen's inverted monument in Gujarat. Mosques on a Kazakh plateau timed to the sun, monolithic churches quarried out of an Ethiopian hillside, a cathedral inside a mountain that never stops moving, and a mining town in the Australian desert with a bookshop underground. Different continents, different centuries, no contact between most of them, and they were all answering the same equation, which is the answer to the question we started with. People go into the ground when the surface becomes more expensive, more dangerous or more uncomfortable than the rock. That is it. That is the entire rule, and it has held for at least 3,000 years without a single exception. Every one of these places is what happens when somebody ran the numbers on staying up top and did not like the

result. Sometimes the cost was an army on the horizon. Sometimes it was persecution, or a siege, or the price of keeping oil from spoiling, or a water table that dropped 15 metres every dry season. Sometimes it was a religious institution deciding that permanence and silence were worth years of chiselwork. Right now, in Australia, it is a power bill and a 50-degree afternoon, and in Finland it is the fact that a city has run out of surface and still needs somewhere to put a water treatment plant. The motives get rewritten every few centuries. The arithmetic does not. There is one more thing worth sitting with before we finish, and it is the part that I find genuinely difficult to shake. Everything we have looked at today was made by people removing material and leaving a shape behind, and a shape made of absence is almost invisible from above.

No walls to spot from a distance, no profile on the horizon, nothing for aerial survey to catch. A city carved into rock leaves no ruins, because there was never anything to fall down. It simply waits, at the same temperature, in the same darkness, in exactly the condition it was left in, for as long as it takes. which means the map is not finished. Not remotely. Turkey alone has hundreds of documented underground settlements and a strong professional suspicion that the documented ones are simply the ones with an entrance nobody managed to close. The largest complex on that list only entered the record because a municipal work crew was tidying up a historic street a handful of years ago and the majority of it is still sitting there, unexcavated under houses where people are getting on with their evening right now.

So the next one is not going to be found by an expedition. It is going to be found by a water main bursting, a car park being extended, a foundation survey for a new apartment block, or somebody digging a hole in their own garden for entirely ordinary reasons. It has happened that way over and over, and there is no argument for assuming it has stopped. Under whatever street you happen to be standing on, there are kilometres nobody has walked. Somebody has probably already been down there a very long time ago and left it exactly as they found it. If you know of something under your own town, a tunnel, a sealed cellar, a local story everyone repeats and nobody has checked, put it in the comments because those stories are how most of these places got found in the first.

Two and five Canadians will hear the words, you have cancer. That's why every step and dollar raised matters. On September 19th, join thousands in Toronto for the Princess Margaret Cancer Foundation Walk. Challenge yourself, friends, and family to walk 21 kilometers in support of life-saving research. Together, we can carry the fire and help create a world free from the fear of cancer. Register today at pmcf walk.ca. Real Canadian Superstore has everything you need this back-to-school season. Save on lunchbox savers like Ziggy's sliced deli-meat products for always 375.

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