Hey everyone, welcome back to My Weird Prompts. I am Corn, and I am sitting here in our living room in Jerusalem with my brother.
Herman Poppleberry, at your service. And Corn, I have to say, the energy in the house has been a little different lately. Our housemate Daniel has been spending quite a bit of time in the underground car park downstairs because of the recent rocket alerts, and it has clearly got him thinking.
It really has. He sent us this prompt today that is honestly a bit of a pivot from our usual surface level discussions. He was telling me the other day that after spending a few hours down there among the concrete pillars and the fluorescent lights, he started wondering if this is just our future. Not just as a temporary shelter, but as a permanent way of life. You know the feeling, Herman. You are sitting on a plastic chair, the air smells like damp limestone and old exhaust, and you look up at the ceiling and realize there are six stories of residential apartments above you, and you feel... strangely safe, but also deeply disconnected.
It is the Jerusalem Car Park paradox. These spaces are our most vital survival assets during a crisis, yet they are the most neglected architectural spaces we own. They are gray, they are windowless, and they are usually filled with junk. But Daniel’s point was: why is the safest place in the city also the place where nobody wants to be for more than an hour? We are seeing a massive shift in urban planning right now, moving away from that old bunker mentality where the underground is just a hole to hide in, and toward a vision of urban expansion where the future of the city is down, not up.
Today we are doing a deep dive, quite literally, into the technical, physiological, and economic feasibility of transitioning from emergency subterranean shelters to permanent, high-density urban living. We are moving beyond the bunker and looking at subterranean urbanism as a legitimate frontier for city planning. We are asking if we can turn Daniel’s car park into a neighborhood.
I love this topic because it forces us to confront the difference between surviving and thriving. It is one thing to sit in a car park for forty-five minutes waiting for an all-clear signal. It is an entirely different thing to sign a thirty-year mortgage on a three-bedroom apartment that is sixty feet below the street level. To get our heads around this, we have to define what we mean by Subterranean Urbanism. We are not talking about basements or wine cellars. We are talking about master-planned, multi-level city layers that function as a cohesive ecosystem.
And to understand where we are going, we have to look at where we have been. The historical pivot here is fascinating. When most people think of underground cities, they think of Cappadocia in modern-day Turkey. Specifically the city of Derinkuyu. This was a massive complex carved into soft volcanic rock that could house up to twenty thousand people.
And it was not just a series of caves, Corn. It was sophisticated. They had ventilation shafts that went as deep as eighty meters. They had wineries, oil presses, stables, and even chapels. But the driver there was pure necessity. It was a refuge from persecution and warfare. You could roll these massive, five-hundred-kilogram circular stone doors shut from the inside, and you were essentially invisible to an invading army. But here is the catch: they did not live there permanently by choice. It was a seasonal or emergency measure. Once the threat passed, they went back to the surface to breathe the air and farm the land.
Contrast that with the modern leaders in this space, like Helsinki, Finland. They have moved far beyond the survival-based refuge. Helsinki has an actual Underground Master Plan, which they have been refining for years. They have mapped out the bedrock to create a second city layer that is integrated into daily life.
Right, and the philosophy there is dual-use. In Helsinki, you have these massive underground spaces that serve as swimming pools, go-kart tracks, and data centers on a Tuesday afternoon. But within hours, they can be converted into civil defense shelters for thousands of people. It is a brilliant way to justify the cost. You are not building a "dead" space that sits empty ninety-nine percent of the time. You are building a vibrant part of the city that just happens to be under the granite.
But that brings us to the biggest hurdle, which is the human element. Even if the space is beautiful, can we actually live there? This is where we get into the Circadian Paradox. Humans have evolved over millions of years to be tethered to the sun. We have an internal clock, the suprachiasmatic nucleus, which is a tiny clump of cells in the hypothalamus that responds to light signals from our eyes.
And when you take that light away, everything drifts. Corn, you were looking at that study from early two thousand twenty-four, right?
Yes, a major paper published in Frontiers in Nutrition. They were looking at the direct link between vitamin D deficiency and the destabilization of sleep and mood. It is not just about being tired. Vitamin D plays a crucial role in the synthesis of serotonin and melatonin. The study found that without natural light exposure, the body’s ability to regulate its own happiness and rest cycles begins to degrade within days.
This reminds me of the baseline experiments by Michel Siffre back in nineteen sixty-two. He was a French geologist who spent two months living in total isolation in an underground glacier. No clock, no sun, no outside contact. He just ate and slept when his body told him to.
And his perception of time completely shattered. When his team finally called him to come out after sixty days, he thought only thirty-five days had passed. His internal clock had stretched. Most humans, when deprived of external cues, fall into a free-running rhythm of about twenty-five hours, not twenty-four.
So, if Daniel moves into a permanent subterranean apartment, he is basically living in a permanent state of jet lag. His body wants a twenty-five-hour day, but the surface world is running on twenty-four. Within a month, he would be trying to eat breakfast at three in the morning while the rest of Jerusalem is asleep.
It is even more intense than that. There was another experiment in nineteen eighty-nine with an Italian interior designer named Stefania Follini. She spent one hundred and thirty days in a cave in New Mexico. Her cycle drifted so far that her "day" eventually became forty-four hours long. She would stay awake for twenty-three hours and then sleep for ten. Her immune system weakened, and her mood plummeted.
So the question is: can we hack this? Can we use technology to trick the suprachiasmatic nucleus?
We are trying. Architects are now looking at circadian-synced environmental controls. This means using full-spectrum LED lighting that changes color temperature throughout the day—shifting from cool blues in the morning to warm ambers in the evening to mimic the sun. But the Frontiers in Nutrition study suggests that supplements and LEDs might not be enough. There is a psychological phenomenon called sky-hunger.
Sky-hunger. That is a visceral term.
It is. It is the biological need for a visual connection to the atmosphere. We are programmed to need a horizon. Without it, the brain experiences a constant, low-level stress response. It is a form of environmental claustrophobia. And that leads us to a staggering statistic from a two thousand twenty-three survey: forty percent of urban residents associate underground spaces with immediate safety risks or claustrophobia.
Forty percent. That is a massive market barrier. If nearly half of your population is biologically or psychologically predisposed to hate your product, your underground city is dead on arrival. So, how do the engineers solve for that? How do we give people a horizon when they are sixty feet under a parking lot?
Well, Herman, that is where the engineering gets really high-tech and, frankly, very expensive. To solve the psychological issue, architects are looking at biophilic subterranean design. This involves things like virtual windows, which are high-resolution screens that sync with real-time weather data from the surface. If it is a dusty, Hamsin day in Jerusalem, your virtual window shows that orange haze. If it is raining, you see the droplets.
But isn't that just a glorified television? Does the brain actually fall for it?
To an extent, yes, but the more effective method is physical photon transport. There are systems now that use parabolic collectors on the roof of a building to track the sun and funnel actual, physical sunlight down through a cable made of optical fibers. You can literally pipe the sun three stories underground. You could have a living olive tree in a basement as long as you have enough fiber-optic cables bringing in the rays.
That changes the vibe from a bunker to a garden. But then you hit the structural realities. Ventilation is the big one. In a normal building, you open a window. In a subterranean city, every breath you take is a product of mechanical engineering. You need massive air handling units, redundant power systems, and sophisticated filtration to prevent something called sick building syndrome, where stagnant air and mold create a toxic environment.
And let's talk about the money, because this is where the "Cost Inversion" comes in. Herman, you were looking at the numbers for some of these big tunneling projects.
It is eye-watering, Corn. If you look at the Suburban Rail Loop in Melbourne, Australia, or some of the deep-bore projects in Singapore, the costs are frequently exceeding one billion dollars per kilometer. One billion per kilometer. For context, you could build several massive skyscrapers for the price of one short tunnel.
So why would anyone do it?
Because of the Cost Inversion. In cities like Singapore, Tokyo, or Manhattan, the cost of surface land has become so astronomical that the one-billion-dollar-per-kilometer price tag for a tunnel is starting to look competitive. If you can't buy any more land on the surface because it is all gone, you have to create land where none existed. You are not just buying a tunnel; you are buying volume.
Singapore is the gold standard for this. They are a tiny island nation with zero room to grow outward. They have already pushed their coastline out as far as they can with land reclamation. So their Urban Redevelopment Authority has a Master Plan for twenty-twenty-five that treats the underground as a primary resource. They are moving their entire sewerage system into deep tunnels—the Deep Tunnel Sewerage System, or DTSS.
And by moving that infrastructure underground, they are freeing up hundreds of acres of prime surface land for housing and parks. It is the "Borrowed from Necessity" pattern. Subterranean expansion almost always starts with the stuff we don't want to look at. Sewers, power lines, subways, and trash. Once you have the tunnels for the infrastructure, you start adding the people.
It is like a gateway drug for urban planning. First, you put the train underground. Then you realize the commuters need a place to buy coffee, so you build an underground mall. That is exactly how Montreal's RESO started. It is one of the largest underground pedestrian networks in the world—over thirty kilometers of tunnels connecting shopping centers, hotels, banks, and universities. People use it to escape the brutal Canadian winters. You can spend your entire day living, working, and eating underground without ever putting on a coat.
But even in Montreal, most people go home to a surface-level apartment. To make the jump to permanent living, we need the "Self-Healing City" tech. This is some of my favorite new engineering. Because we are in Jerusalem, which is a hilly, rocky city, if you dig a deep hole, you are basically creating a bucket for groundwater.
How do you keep Daniel’s apartment from becoming a swimming pool?
Self-healing concrete. This involves concrete that contains dormant bacteria, specifically Bacillus pseudofirmus. These bacteria are mixed into the concrete along with capsules of calcium lactate. When a crack forms and water seeps in, the water activates the bacteria. They eat the calcium lactate and produce limestone, which physically seals the crack from the inside. It is a biological immune system for a building.
That is incredible. So the building literally heals its own wounds. And combine that with LiDAR-driven utility mapping, which we talked about in episode eight hundred twenty-seven. We can now use light detection and ranging to create a perfect three-dimensional map of what is under the ground before we even start digging. In a city like Jerusalem, that is vital because every time you dig a hole, you hit a two-thousand-year-old wall or a Roman cistern.
We talked about that in episode four hundred eighty-one, when they were excavating the Pilgrimage Road. They are digging under people's houses in Silwan, and every inch is a technical and political nightmare. LiDAR allows us to see the "invisible city" and plan our subterranean neighborhoods without destroying history or hitting a main water line.
So, let's look at the takeaways here. If we are moving from "bunker" to "neighborhood," what does that actually look like for the average person?
The first takeaway is the "Borrowed from Necessity" pattern. If you want to know if your city is going underground, look at its infrastructure. If they are moving the sewers and the trains down, the people are next. Second, we need to prioritize Biophilic Subterranean Design. We cannot just build concrete boxes. We need green walls, fiber-optic sunlight, and "horizon-fix" technology—like actual periscopes that bring a real-time view of the sky into the deep levels.
And third, look for cities with an actual Underground Master Plan. Helsinki and Singapore are the leaders because they coordinate their infrastructure. If your city is just letting developers dig random basements, it is going to be a mess. A successful subterranean city needs to be a single, cohesive map.
But Corn, we have to address the ethical elephant in the room. If we do start moving things underground, who gets to stay on the surface?
That is the dark side of this. We could create a new kind of urban inequality. A literal class divide based on elevation. It is the Morlock and Eloi scenario from H.G. Wells. Does the surface become a luxury for the wealthy—with their parks and their natural sunlight—while the working class is relegated to the "deep-zones" where they have to rely on fiber-optic cables and vitamin D supplements?
Imagine the health outcomes for children raised in a subterranean neighborhood versus those raised with natural sunlight. Even with the best LEDs, the developmental differences could be profound. This is why the Helsinki Model is so important. They don't treat the underground as a second-class space. They treat it as a high-quality civic asset. Their underground swimming pools are some of the most beautiful in the city. If you make the subterranean space a place where people want to go, rather than a place they are forced to go, you avoid that social stigma.
But I still think about Daniel in that car park. Even if it was the nicest car park in the world, after three days, he would be clawing at the walls to see the sky. I think the psychological barrier is much higher than the engineering one. We are creatures of the horizon. We need to see the edge of the world to feel like we are part of it.
I agree. I think the future isn't a total move underground, but a hybrid model. I think we will see "inverted" buildings. Imagine a building that is forty stories tall, but twenty of those stories are below ground. The bottom floors are for data centers, automated warehouses, and gymnasiums. The middle floors are for offices and retail. And the top floors, with the windows and the balconies, are for living.
That makes a lot of sense. You use the subterranean space for the functions that don't require a view. My car doesn't need to see the sunset. My server rack doesn't need vitamin D. By moving those functions down, you make the surface level more habitable for humans. You reduce the height of the buildings, you create more space for parks, and you reduce the noise and heat of the city.
It is about optimizing the volume of the city, not just the surface area. We have been stuck in this flat-land mindset for a long time. But if we start treating the first hundred meters of the crust as usable space, we effectively double the size of our cities without expanding the footprint.
It is a more three-dimensional way of thinking about urbanism. And for a city like Jerusalem, that is huge. We have so much history on the surface that we can't build over. If we want to modernize without destroying the soul of the city, going down might be the only ethical way to grow.
So, if the surface becomes uninhabitable due to climate change or conflict, is the underground a sanctuary or a trap? That is the question we have to leave you with. On the surface, if the power goes out, you still have air and light. In a deep subterranean city, if the power goes out and the backup generators fail, you are in a tomb within hours. The level of redundancy required for a permanent underground neighborhood is far higher than for a skyscraper.
It is a high-stakes way to live. Well, this has been a fascinating look into a world that is right beneath our feet. If you enjoyed this dive into the deep, you should definitely check out some of our related episodes.
Yeah, episode eight hundred twenty-seven on mapping the invisible city is a great technical companion. And episode four hundred eighty-one on the engineering of Jerusalem's Pilgrimage Road really puts the "depth" of our city's history into perspective.
And hey, if you have been listening to My Weird Prompts for a while and you haven't left us a review yet, we would really appreciate it. A quick rating or a review on your podcast app, especially on Spotify, really helps new listeners find the show. We see every one of them and it genuinely makes a difference for us.
It really does. And don't forget to head over to myweirdprompts dot com. You can find our full archive there, plus our RSS feed and all the different ways to subscribe. If you are on Telegram, just search for My Weird Prompts to get a notification every time a new episode drops.
Well, thanks for joining us today on this journey into the earth. We will be back next week with another prompt from Daniel, hopefully one that involves a bit more sunshine.
Until then, keep looking up... and maybe a little bit down. This has been My Weird Prompts.
Thanks for listening, everyone. We will talk to you soon.
Goodbye from Jerusalem!
So, Herman, if we actually had to move the podcast studio into the car park, how many fiber-optic cables would you need for your donkey brain to feel happy?
At least a dozen. And I would need a very large virtual window showing a field of grass. A donkey has needs, Corn. A sloth like you would probably just sleep through the entire circadian shift anyway.
You are not wrong. I am already on a twenty-five-hour clock. I was born for subterranean living.
That explains so much about your morning routine. Alright, let's get out of here before you start digging a hole in the living room floor.
Too late, I already started. I think I found a Roman coin.
That is just a bottle cap, Corn. Let's go.
A very historical bottle cap. Bye everyone!
Take care!
One last thing before we sign off completely. We really do want to thank our sponsor, Modal. They are the ones who keep the lights on—full-spectrum or otherwise—by providing the serverless GPU platform that runs our entire generation pipeline. If you are a developer looking for a way to run your models without the headache of managing infrastructure, check out Modal dot com. They are the best in the business.
They make the complex stuff feel simple, which is exactly what we try to do here. Alright, that is the actual end. See you next time!
Bye!
Goodbye!
I still think it is a Roman coin.
It says Coca-Cola on it, Corn.
Ancient Coca-Cola. Very rare.
We are leaving now.
Okay, okay. See ya!
