Deep beneath the city of Prague is another city altogether, one that most people are completely unaware of, and that they’ll hopefully never see. It is a system of hundreds upon hundreds of concrete bunkers with their own electricity, water and ventilation systems awaiting the day that you might hear the air-raid sirens wailing.

Air raid sirens are normal enough in Prague; they are heard all over the city on the first Wednesday of every month at noon when they are tested. The system of bomb shelters is in a similar state of readiness. In the event of a war, there is room beneath the city for 40% of the population. In peacetime however, the countless kilometres of tunnels are inhabited only by a few dozen workers of the town hall’s shelters administration department. Deep beneath Prague, they keep the bunker system in tip-top shape from day to day, hoping at the same time it will never be used. Mr Rostislav Guth is in charge of the department.

The pedestrian tunnel under Vítkov hill

One of the larger shelters is under Vítkov Hill. At the end of an alley there is a pedestrian tunnel through the hill, and in the middle of that is an inconspicuous door that leads to a forgotten world. This bunker is a series of extremely long corridors with a long incline, about three to four metres high and painted white and pastel green, the way communist-era hospitals and prefab stairwells were. If you have ever been inside an old WWII battleship for example, the atmosphere is similar, with an omnipresent smell of grease, mould and paint. It’s not the kind of place you would want to spend a lot of time in, but then even if there were a war, you wouldn’t have to:

“These shelters were made for people to be able to survive here for 72 hours. Of course, everything ultimately depends on the type of attack we would face, but 72 hours was considered enough time for safety measures to be taken on the surface, enough time for them to be able to get to the people inside the shelter if it were buried in debris and the optimum period in terms of food stores and so on.”

Going into the Prague bunkers is a literal descent into history. Key to the general ambience are the technological relics kept in perfect working order. The machinery is almost all from the 1950s, great big objects piped into the walls with huge bakelite knobs, and needle gauges. Everything is of massive design, even the ancient telephones hanging from the walls, and of course the ventilation system, the noise of which would probably drive one mad within less than 72 hours.

“The ventilation system takes in air from outside through these filters and it creates overpressure in the shelter. The shelter is then ‘inflated’, so to speak, and weaponised gases or toxic substances wouldn’t be able to get in thanks to the overpressure created by the ventilation system and the filters.”

The hundreds of metres of empty white tunnels, fluorescent lights and grey pipes are ready to become a makeshift home for 1,250 people at any given moment. Everything is meticulously cared for – the staff was particularly pleased that I was unable to record any creaking and thudding sounds off the heavy bulkheads that divide the shelter up, because they’re so well oiled. With that kind of readiness, I half-expected to see mounds of powered milk and canned plums – but I came a few decades late for that.

But again, sprawling though it may be, the Prague bunker system is only big enough for 40% of the population - roughly less than half-a-million people. Certainly even less than that number though is even aware of what all is under their feet. In the event of a war, I thought, few would know where to go, and if they did, they wouldn’t be room for them all.

“It depends on the so-called “running distance”, the shelters are designed to hold the population within a 15-minute running distance, and that’s established during peacetime. For example schools know which shelter to take the children to even now in peacetime. Others would have to use improvised shelters. If there were a threat to the country, cellars and underground garages would be fortified. We always check new buildings, new office buildings for example, to make sure their underground spaces can be converted into shelters with air filters and so on in the event of a war. They wouldn’t be pressure-resistant, but people would be able to wait out an air raid there.”

The city’s emergency services would rely on notification systems established during the Second World War. Each district has a plan for sending its citizens to the appropriate shelter. Emergency workers would be stationed around the city to help people orient themselves. The bunkers themselves would have to be not only stocked but also cleared out within 24 hours, as many are rented out as storage space. And perhaps even more difficult to imagine, the underground transportation services – the metro and tunnels – would be transformed into a living space for tens of thousands of people.

“Strahovský Tunnel is the largest makeshift shelter and it can shelter 15,000 people, if I leave aside the metro. Both have technical and medical facilities running along the sides of the tunnels, and the tunnels then would hold the people. The two ends of Strahovský Tunnel would be sealed; the metro can be closed off every two stations. You can see it when you enter the stations: big, heavy parts of the door that would seal the station off. Or at least I see them because I’m in the business, everyday citizens probably don’t notice them.”

In any case, if bombs start falling out of the sky over the Czech Republic you’ll be better off squeezing into a bunker in Prague than anywhere else in the country. While most people in the capital would find shelter somewhere, elsewhere in the country there is only room for 12% of a population of 10 million – small in comparison to other European countries of similar size.

It’s all so otherworldly, at the end of the day: a city under a city in a peaceful European state, ready to house its people from nuclear Armageddon or other such nastiness; Czechs in gas masks wandering up into a bombed out Prague after 72 hours in 1950’s bunkers. It’s almost as scary as the fact that it happened before, over sixty years ago, and the people who work in the bunkers have little trouble visualising it again.

“It can certainly be imagined. These bunkers are made for war, and in a time of war they will work. So we can imagine it.”