Secret Military Aerodrome, Željava, Border of Croatia and Bosnia-Herzegovina, 2025

As a non-aligned country Yugoslavia strode the Cold War border between NATO and Soviet Blocs. Built deep into the mountainside the concealed concrete aircraft hangars, bunkers, and extensive tunnel networks at Željava could withstand a direct hit from a 20 kiloton atomic bomb. 

Part of the secret network of Objekat military installations throughout Yugoslavia. During the fall of Yugoslavia, the installation was initially used as an operational base by Serb forces. Retreating before the eventual advance of the Croatian army, the Serbs rendered the base inoperable by Croat forces, through dynamiting. It is advisable to keep to asphalted paths, runways, and roads as there are significant numbers of unexploded mines in the area.