The Armijska Ratna Komanda D-0, also known as the Ark, was a Cold War-era nuclear bunker and military command centre located near the town of Konjic in Bosnia and Herzegovina. Built to protect Yugoslav President Josip Broz Tito and up to 350 members of his inner circle in the event of an atomic exchange, the structure is made up of residential areas, conference rooms, offices, strategic planning rooms, and other areas. The bunker remained a state secret until after the breakup of Yugoslavia in the 1990s.
The facility is now under the authority of the Bosnian Ministry of Defense and is managed by the country's military, guarded by a five-soldier detachment, but is designated by KONS as National Monuments of Bosnia and Herzegovina and used as exhibition space for project such as Cultural Event of Europe with strong UNESCO support, and tourist attraction.
Another underground facility is Željava Air Base, situated on the border between Bosnia and Herzegovina and Croatia under the  mountain, near the city of Bihać. It was the largest underground airport and military air base in the Socialist Federal Republic of Yugoslavia (SFRY), and one of the largest in Europe. The role of the facility was to establish, integrate and coordinate a nationwide early warning radar network in SFRY akin to NORAD in the US. The complex contained tunnels in total length of 3.5 km (2.2 mi), and the bunker with four entrances protected by 100-ton pressurized doors, three of which were customized for use by fixed-wing aircraft. capable in housing two full fighter squadrons, one reconnaissance squadron, and associated maintenance facilities. It was designed and built to sustain a direct hit from a 20-kiloton nuclear bomb, equivalent to that dropped on Nagasaki. The underground facility was lined with semicircular concrete shields, arranged every 10 km (6.2 mi), to cushion the impact of incoming strike. The complex included an underground water source, power generators, crew quarters, and other strategic military facilities. It also housed a mess hall that could feed 1,000 people simultaneously, along with stores of food, fuel and arms sufficient to last 30 days. Fuel was supplied by a 20 km (12 mi) underground pipe network connected to a military warehouse on Pokoj Hill near Bihać. Nowadays, they are popular for urban exploration.