In 1953, President Tito of Yugoslavia ordered a massive nuclear bunker to be built. The called Atomska Ratna Komanda (Ark) was constructed an hour south-west of Sarajevo.
Tito's ARK is thought to be the largest underground military developement within Bosina and Herzegovina. And if it were restocked with supplies today, 350 people would be able to live and work for six months without ever having to leave its confines.
Mega Builds is a video series from BBC Future looking at giants of engineering from around the globe.
Video script: Arabella Turek, from the Department of Science and Technology Studies, University College London.