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 October 19, 2015. Artillery fort Faulensee was in military use from 1943 to 1993 and is now open to the public as a museum. With the threat of foreign invasion a thing of the past, thousands of military bunkers and fortresses in Switzerland have been put to commercial use, from hotels to data centres, museums to cheese factories. The Swiss army has sold most of these decommissioned strongholds, but about a thousand unused bunkers remain, many still disguised as houses and barns. (Photo by Arnd Wiegmann/Reuters)





A former infantry bunker camouflaged as a medieval house is reflected in a mirror in Duggingen, Switzerland August 19, 2015. With the threat of foreign invasion a thing of the past, thousands of military bunkers and fortresses in Switzerland have been put to commercial use, from hotels to data centres, museums to cheese factories. (Photo by Arnd Wiegmann/Reuters)





The view through the muzzle of a 10.5cm gun is seen at a bunker at the former artillery fort of the Swiss Army in the town of Faulensee, Switzerland October 19, 2015. (Photo by Arnd Wiegmann/Reuters)





A 10.5cm gun stands in a bunker at a former Swiss Army fort in the town of Faulensee, Switzerland October 19, 2015. (Photo by Arnd Wiegmann/Reuters)





The muzzle of a 15cm gun is seen at the former Swiss artillery fortress Sasso da Pigna at the St. Gotthard mountain pass, Switzerland September 2, 2015. Sasso da Pigna fortress, located at 2,106 m (6,909 ft) altitude on the St. Gotthard mountain pass was built from 1941 to 1945 and was in military use until 1999. Since 2012 it has been open to the public as Sasso San Gottardo museum. With the threat of foreign invasion a thing of the past, thousands of military bunkers and fortresses in Switzerland have been put to commercial use, from hotels to data centres, museums to cheese factories. (Photo by Arnd Wiegmann/Reuters)





A view shows the restaurant at the Hotel La Claustra in a former Swiss army bunker on the St. Gotthard mountain pass, Switzerland August 8, 2014. With the threat of foreign invasion a thing of the past, thousands of military bunkers and fortresses in Switzerland have been put to commercial use, from hotels to data centres, museums to cheese factories. (Photo by Arnd Wiegmann/Reuters)





Cyclists ride past the Hotel La Claustra located in a former bunker of the Swiss army on the St. Gotthard mountain pass, Switzerland August 8, 2014. (Photo by Arnd Wiegmann/Reuters)





Barbed wire protects a bunker at former Swiss artillery fortress Reuenthal near the village of Reuenthal, Switzerland 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. (Photo by Arnd Wiegmann/Reuters)





A flag flies over an entrance to the former Swiss artillery fortress Sasso da Pigna at the St. Gotthard mountain pass, Switzerland September 2, 2015. Sasso da Pigna fortress, located at 2,106 m (6,909 ft) altitude on the St. Gotthard mountain pass, was built from 1941 to 1945 and remained in military use until 1999. (Photo by Arnd Wiegmann/Reuters)





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 October 27, 2015. (Photo by Arnd Wiegmann/Reuters)





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 August 29, 2015. In eleven former bunkers Gotthard-Pilze produces some 24 tons of shiitake mushrooms per year. (Photo by Arnd Wiegmann/Reuters)





A former control room is seen at a decommissioned Swiss military command bunker near Attinghausen, Switzerland September 2, 2015. Deltalis data centre offers high-security storage of data in server rooms inside the former command bunker, which was built in 1948. (Photo by Arnd Wiegmann/Reuters)





A view shows an operating room at the former Swiss artillery fortress Reuenthal near the village of Reuenthal, Switzerland 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. (Photo by Arnd Wiegmann/Reuters)





Bunkers at former Swiss artillery fortress Reuenthal are seen on a hill near the village of Reuenthal, Switzerland November 18, 2014. 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. (Photo by Arnd Wiegmann/Reuters)





A bunker at aformer Swiss artillery fortress called Heldsberg stands near the town of St. Margareten, Switzerland March 22, 2015. Heldsberg fortress, located on the Swiss-Austrian border near the River Rhine and Lake Constance was built from 1938 to 1940 and remained in military use until 1992. Since 1993 it is open to the public as Fortress Museum Heldsberg. (Photo by Arnd Wiegmann/Reuters)





A former infantry bunker is camouflaged as a medieval house in the town of Duggingen, Switzerland August 19, 2015. (Photo by Arnd Wiegmann/Reuters)





A tunnel connects the bunkers at a former Swiss Army artillery fort in Faulensee, Switzerland October 19, 2015. Artillery fort Faulensee was in military use from 1943 to 1993 and is now open to the public as a museum. (Photo by Arnd Wiegmann/Reuters)





An artillery control room is seen in a bunker at a former artillery fort in the town of Faulensee, Switzerland October 19, 2015. (Photo by Arnd Wiegmann/Reuters)





Switzerland's national flag is painted on a spare muzzle for a 10.5cm gun at the former artillery fort of the Swiss Army in the town of Faulensee, Switzerland October 19, 2015. (Photo by Arnd Wiegmann/Reuters)





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 August 6, 2015. Fuchsegg fortress, located in the central Swiss Alps, was built in 1943 and remained in military use until 1993. With the threat of foreign invasion a thing of the past, thousands of military bunkers and fortresses in Switzerland have been put to commercial use, from hotels to data centres, museums to cheese factories. (Photo by Arnd Wiegmann/Reuters)





The Urserental valley is seen behind a camouflaged canon at a former Swiss artillery fortress called Fuchsegg near the village of Realp, Switzerland August 6, 2015. Fuchsegg fortress, located in the central Swiss Alps, was built in 1943 and remained in military use until 1993. (Photo by Arnd Wiegmann/Reuters)





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 January 6, 2016. Artillery fort Furggels was in military use from 1946 to 1998 and is now open to the public as a museum. (Photo by Arnd Wiegmann/Reuters)





A sign reads "Military site – Entering and photography forbidden" at former Swiss artillery fortress Sasso da Pigna on the St. Gotthard mountain pass, Switzerland August 6, 2015. Sasso da Pigna fortress, located at 2,106 m (6,909 ft) altitude on the St. Gotthard mountain pass, was built from 1941 to 1945 and remained in military use until 1999. Since 2012 it has been open to the public as Sasso San Gottardo museum. (Photo by Arnd Wiegmann/Reuters)