The Urserental valley is seen behind a camouflaged cannon (lower left) at a former Swiss artillery fortress called Fuchsegg near the village of Realp, Switzerland, on August 6, 2015. Fuchsegg fortress, located in the central Swiss Alps, was built in 1943 and remained in military use until 1993. #

Cows stand in a meadow in front of a 10.5cm gun at the former artillery fort of the Swiss Army in the town of Faulensee, Switzerland, on October 19, 2015. Fort Faulensee was in military use from 1943 to 1993 and is now open to the public as a museum. #

The muzzle of a 15cm gun is seen in a bunker at the former artillery fort Furggels of the Swiss Army near the village of St. Magrethenberg, Switzerland, on January 6, 2016. Fort Furggels was in military use from 1946 to 1998 and is now open to the public as a museum. #

Looking through the muzzle of a 10.5cm gun in a bunker at the former Swiss Army artillery fort in the town of Faulensee, Switzerland, on October 19, 2015. #

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 Realp, Switzerland, on August 6, 2015. #

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 Erstfeld, Switzerland, on August 29, 2015. In eleven former bunkers Gotthard-Pilze produces some 24 tons of shiitake mushrooms per year. #

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 Giswil, Switzerland, on October 27, 2015. #

Barbed wire protects a bunker at former Swiss artillery fortress Reuenthal near the village of Reuenthal, Switzerland, on July 18, 2015. Reuenthal fortress, located on the Swiss-German border near the rivers Rhine and Aare was built from 1937 to 1939 and remained in military use until 1988. Since 1989 it has been open to the public as Fortress Museum Reuenthal. #

A flag flies over an entrance to the former artillery fortress Sasso da Pigna at the St. Gotthard mountain pass, Switzerland, on September 2, 2015. Sasso da Pigna fortress, located at 2,106 m (6,909 ft) above sea level, remained in military use until 1999. Since 2012 it has been open to the public as Sasso San Gottardo museum. #

A former control room is seen at a decommissioned Swiss military command bunker near Attinghausen, Switzerland, on September 2, 2015. Deltalis data center offers high-security storage of data in server rooms inside the former command bunker, which was built in 1948. #

The muzzle of a 15cm gun sticks out a chain-covered opening in the former Swiss artillery fortress Sasso da Pigna at the St. Gotthard mountain pass, Switzerland, on September 2, 2015. #