Any visitor to the Southeast European country of Albania will undoubtedly stumble across one of its hundreds of thousands of concrete bunkers that have dotted the landscape for over six decades.

Norway's proximity to the USSR in the Cold War led to it building many military bunkers – some of them vast secret bases.

South Korea later acquired the GBU-28, deploying 150 units by 2014 to arm F-15K fighter jets in case of a strike on North ...

About 1,000 concrete bunkers with trenches, anti-tank trenches, ammunition storage and supply shelters are part of a joint ...

Tensions with Russia have brought the bunkers back into focus ... with their rough rock walls, gleaming concrete and military equipment. Carved out of a mountain side, protected by around 900ft ...

Potential adversaries may use reinforced concrete with significant ... ideal for destroying fortified bunkers and underground facilities which house sensitive military hardware or command centers.