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. The Swiss army has sold most of these decommissioned strongholds, but about a thousand unused bunkers remain, many still disguised as houses and barns. REUTERS/Arnd Wiegmann PICTURE 10 OF 27 - SEARCH "SWISS BUNKER" FOR ALL IMAGES