During the Second World War, Switzerland had a network of around 8,000 bunkers and military shelters. After Germany invaded France in 1940, the famously neutral Switzerland was surrounded by Axis powers and recognised it would be out-gunned in any assault. To hold off an invasion, Switzerland sought to make itself prohibitively difficult to conquer.

Under a plan dubbed the National Redoubt, much of the country's manpower and firepower would retreat to the mountains if a foreign aggressor attacked. Through its chain of fortresses and bunkers, Switzerland would keep control of the mountains along with key transit routes. During the Cold War, concerns turned to nuclear attack. The Swiss ramped up military spending and many homes were required to be equipped with bomb shelters.

In more recent years, though, due to high maintenance costs and a cooling threat of invasion, the Swiss Army has tasked a property company with trimming the number of bunkers down. Dotted around Switzerland, often disguised as barns and houses, the vast majority have now been bought, sealed off or set aside for historical preservation.

Swiss army bunkers
A machine-gun bunker, part of a former Swiss artillery fortress called Fuchsegg, is camouflaged as a stable beside the Furka mountain-pass road near the village of RealpArnd Wiegmann/Reuters
Swiss army bunkers
A flag flies over an entrance to the former Sasso da Pigna Swiss artillery fortress on the St Gotthard mountain passArnd Wiegmann/Reuters
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A tunnel connects bunkers at a former Swiss Army artillery fort in FaulenseeArnd Wiegmann/Reuters
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A 10.5cm gun stands in a bunker at a former Swiss Army fort in the town of FaulenseeArnd Wiegmann/Reuters
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A former control room is seen at a decommissioned Swiss military command bunker near AttinghausenArnd Wiegmann/Reuters
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The muzzle of a 15cm gun is seen at Sasso da Pigna, a former Swiss artillery fortress on the St Gotthard mountain passArnd Wiegmann/Reuters
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A sign reads "Military site - Entering and photography forbidden" at the Sasso da Pigna fortress on the St Gotthard mountain passArnd Wiegmann/Reuters
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An operating room inside the former Reuenthal Swiss artillery fortressArnd Wiegmann/Reuters
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The muzzle of a 15cm gun is seen in a bunker at the former Furggels artillery fort near the village of St MagrethenbergArnd Wiegmann/Reuters
Swiss army bunkers
A camouflaged 10.5cm gun is seen at the former Furggels fort near the village of St MagrethenbergArnd Wiegmann/Reuters
Swiss army bunkers
An artillery control room is seen in a bunker at a former artillery fort in the town of FaulenseeArnd Wiegmann/Reuters
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Cows stand in a meadow in front of a 10.5cm gun at a former artillery fort in the town of FaulenseeArnd Wiegmann/Reuters
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A former infantry bunker is camouflaged as a medieval house in the town of Duggingen, SwitzerlandArnd Wiegmann/Reuters

Many of the former strongholds have been transformed and refashioned into business such as data centres, hotels, museums and even mushroom farms and cheese factories. Swiss mushroom producer Gotthard-Pilze produces some 24 tonnes of shiitake mushrooms per year in 11 former bunkers.

Swiss army bunkers
Raclette cheeses made by Swiss cheesemaker Seiler Kaeserei AG mature in storage racks in a former ammunition bunker of the Swiss Army in the town of GiswilArnd Wiegmann/Reuters
Swiss army bunkers
Alex Lussi of Swiss mushroom producer Gotthard-Pilze picks a shiitake mushroom inside a former ammunition bunker of the Swiss Army near the town of ErstfeldArnd Wiegmann/Reuters

For upwards of almost $200 a night, guests at a Swiss hotel might expect to catch a glimpse of the towering Alps or overlook one of the country's famous lakes. But visitors to Hotel La Claustra get a room without a view. The 17-room hotel is buried in the Gotthard mountain range and, with cavernous walls and minimalist interior, offers the chance to spend a few nights in an ex-army bunker.

Swiss army bunkers
Cyclists ride past the Hotel La Claustra located in a former Swiss army bunker on the St Gotthard mountain passArnd Wiegmann/Reuters
Swiss army bunkers
The Hotel La Claustra restaurant in a former Swiss army bunker on the St Gotthard mountain passArnd Wiegmann/Reuters