At the peak of the Cold War, the sparsely populated, mountainous country of Norway had around 3,000 underground facilities where its armed forces and allies could hide and make life difficult for any invader. After the USSR fell, these bunkers fell into disuse and some were sold. They are now being repaired and modernized because of Russia's invasion of Ukraine and the Kremlin's growing military build up in the Arctic. For example, the bunker in Bardufoss can keep expensive fighter planes safe from attacks by Russian drones: ichef.bbci.co.uk