A sprawling top secret Danish nuclear bunker opened to the public for the first time on Monday, shedding light on the Nordic country’s emergency provisions during the Cold War.

The underground shelter, where everything is still intact as in a time capsule, was taken out of service in 2003 and first revealed to the world in 2012.

Museum visitors can now walk two kilometres during a 90-minute tour of the bunker in North Jutland’s Roldskoven forest, but the waiting list to see the Cold War facility is considerable according to broadcaster DR.

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Tickets for the museum can be reserved with the Historical Museum of Northern Jutland, which is responsible for the new museum.

But the North Jutland museum is reporting that almost all tickets for visits in the next few months have been snapped up.

“We opened ticket sales on November 1st and have so far sold almost 27,000 of the 28,800 tickets we have put on sale until the summer,” head of publicity Lars Enevold Pedersen told news wire Ritzau.

Space in the nuclear-safe bunker is limited, meaning advance reservations are needed for the tours, which have a capacity of 10 visitors.