The Rold Forest was deemed the optimum location for the Cold War bunker since it's extremely secluded and situated far away enough from Denmark's southern and eastern borders to resist a Soviet invasion, according to YouTube channel Hidden in Sweden.

A staggering 3.2 million cubic feet of rock was blasted away to create the bunker. Work was carried out by local builders and fencing around the complex was minimal to play down the significance of the project. All in all, Denmark's best-kept secret was five years in the making, becoming operational in 1968.

The main entrance is well-camouflaged with overgrown vines. Interestingly, it was the only part of the facility staffed by an armed guard. Given its designation as a civilian installation, weapons were actually banned from the bunker itself. Now, let's step inside.

REGAN Vest: tour Denmark’s secret Cold War bunker built to protect the royal family