Switzerland once had thousands of bunkers hidden in the Alps to guard against foreign invasion during the Second World War. During the Cold War, they remained as bomb shelters in case of nuclear attack.
But with those threats long gone, many of the decommissioned fortresses now serve as everything from cheese and mushroom factories, to museums and hotels.
Underground hotel nestled into rock
It's not apparent from the outside, but this four-star hotel, converted from an underground artillery fort, has 17 rooms, a swimming pool, library, spa and restaurant in Switzerland's Gotthard Pass region.
Subterranean, but not claustrophic
Designer Jean Odermatt included an eery view from the hotel's restaurant.
Cheesy solution to former ammunition bunker
Swiss cheesemaker Seller Kaeserek AG uses this former bunker to produce Raclette cheese in the town of Giswil.
Elsewhere, it's mushrooms
In 11 former bunkers the, company Gotthard-Pilze produces some 24 tonnes of shiitake mushrooms per year.
Turret-mounted long guns
This one-time artillery fort was meant to defend Switzerland against a Nazi invasion and was built in 1942.
Ready for an invasion that never happened
Artillery control room-turned-museum
This one-time bunker in Faulensee was operational from 1943 to 1993.
Swiss defence included tunnels
This tunnel connects underground bunkers in the town of Faulensee. The system was built to defend against an invasion by German forces that was planned but never carried out.
Sasso da Pigna artillery fort at 2,106 metres
Construction of this gun fortress took place from 1941 to 1945, and was in military use until 1999. Since 2012, it has been open to the public as the Sasso San Gottardo museum.
Nothing out of the ordinary here
But what appears to be a stable was actually once a machine-gun fortress called Fuchsegg. It stands beside the Furka mountain-pass road near the village of Realp in the central Swiss Alps. It was built in 1943 and remained in military use until 1993.