Fun Fact: In WWII the entire country of Switzerland was basically just one giant underground fortress.
Indeed! Most interesting are the camouflaged bunkers of those fortresses which were used and improved throughout the cold war. Here are some astonishing examples...
Military bunker in Hilterfingen/Swiss. The complete exterior is painted, even the windows.
An infantry-bunker camouflaged as a villa in Gland/VD. Today it is a museum.
Artillery gun camouflaged as rocks at the fortress of San Carlo.
Bunkers and artillery guns camuolflaged as stables, barns and sheds.