If you were led into it blindfolded, you might take it for a particularly luxurious block of flats. The apartments, complete with marble-topped kitchen counters, sell for up to $4.5 million (3.4m). One is designed like a log cabin, with a window looking out on snowy mountains. There is a cinema, a gym, a library, and a swimming-pool. But these are flats with a difference: they are all deep underground.

Created by veteran property developer Larry Hall, the Survival CondoShort for "condominium". It means a set of flats owned by different people. apartments occupy what used to be a nuclear-missile silo in Kansas. Protected by nine feet of concrete and remote-controlled machine guns, and descending through 15 storeys, they are designed to keep a community of 75 people alive for five years after the world has collapsed into chaos.

Larry Hall is - in the words of Bradley Garrett's book, Bunker: Building for the End Times - a "doom merchant", profiting from people's fear of catastrophe. The US alone is thought to have 3.7 million so-called "preppers", preparing for doomsday by buying subterranean refuges and stocking up on arms and necessities. Between them, they spend $400 million a year on emergency food supplies. Thailand and New Zealand are among the destinations favoured by the ultra-rich.

The world's biggest "survival community", Vivos xPoint in South Dakota, covers 18 square miles, making it almost three-quarters the size of ManhattanAn island formed by three rivers which is the centre of New York City.. It contains 575 private bunkersReinforced underground shelters. The term comes from an old Swedish word for boards used to protect the cargo of a ship., with room for 10,000 people, linked by 100 miles of private road.

Humans have long put their faith in underground dwellings. In CappadociaA large central region of what is now Turkey, consisting of a high plateau with volcanic peaks., there are 22 complexes dug into the hills by the HittitesA race that created an empire in Asia Minor in around 1,600BC. It was overrun by the Assyrians four centuries later. in around 1,200BC, with the deepest one accommodating as many as 20,000 people.

Bradley Garrett dates the modern "doom boom" from the Cuban missile crisisA confrontation between the US and the Soviet Union that occurred after the USSR installed missiles on the island of Cuba, within 140km of Florida. in 1962, when the US government encouraged people to build their own nuclear shelters. There was a further surge after 11The phone number of emergency services in the USA. In the UK, it is 999. , and now - thanks to global warming, civil unrest, and the pandemic - there is another. The creator of xPoint, Robert Vicino, claims that bunker sales have increased by 600% this year.

What you get for your money varies enormously. At Vivos xPoint, it is simply a concrete and steel bunker with plumbing and electricity, designed to withstand a 500,000-pound blast. For some, this is enough: "I just love my bunker," IT consultant Milton Torres told Garrett. "I close the door and stay in there for a few days and then I can think again."

Larry Hall, on the other hand, has worked with psychologists to make life at Survival Condo seem as normal as possible. "No one wants to be reminded all the time that they are basically living in a submarine," he says. Hence the apartments' "windows" - in fact, LED screens which display whatever scenes the owners choose. One owner, Garrett reports, has a series of videos of Central Park taken from her New York flat "during all four seasons, day and night, together with the cacophonousOriginally a Greek word, it means horrible to listen to. sounds of urban life".

Some, including Bradley Garrett, say yes. The world is an increasingly unstable place in terms of politics, climate change, and health. The way in which our lives have been turned upside down by the pandemic is an indication of what might lie ahead. We will all have to rely on ourselves when the moment comes, so it is only sensible to take precautions.

Others argue that preppers are behaving as if society were bound to collapse and, if everyone cut themselves off in the same way, this would become a self-fulfilling prophecySomething that happens because enough people are persuaded that it will.. As the pandemic has shown, the way for humans to get through a crisis is as a community, with everyone acting unselfishly. Taking an optimistic view will give us the courage to carry on and find solutions to our problems.

Condo - Short for "condominium". It means a set of flats owned by different people.

Manhattan - An island formed by three rivers which is the centre of New York City.

Bunkers - Reinforced underground shelters. The term comes from an old Swedish word for boards used to protect the cargo of a ship.

Cappadocia - A large central region of what is now Turkey, consisting of a high plateau with volcanic peaks.

Hittites - A race that created an empire in Asia Minor in around 1,600BC. It was overrun by the Assyrians four centuries later.

Cuban Missile Crisis - A confrontation between the US and the Soviet Union that occurred after the USSR installed missiles on the island of Cuba, within 140km of Florida.

911 - The phone number of emergency services in the USA. In the UK, it is 999.

Cacophonous - Originally a Greek word, it means horrible to listen to.

Self-fulfilling prophecy - Something that happens because enough people are persuaded that it will.