That door finally swung open last week—nine years after this cold war relic had been consigned to history—as the German government broke ground on a project to turn the bunker into a museum. “People were very curious to see this secret place,” said Florian Mausbach, the president of the Federal Authority for Construction and Urban Planning, which is overseeing the project. “I was struck by the idyllic scenery outside and the nightmare-like atmosphere inside.”

Venturing into the labyrinth of dark tunnels is like wandering onto a set for Dr. Strangelove, long after the lights have been switched off. Radiation decontamination rooms line the entrance hall. Black air horns hang on the walls, ready to bleat a signal that the 25-ton bombproof doors are about to shut. Signs warning of “lebensgefahr,” or danger, are everywhere.

By early 2008, visitors will be able to stroll through a 656-ft stretch of tunnel, which will be restored to its vintage state. An adjoining visitor center will feature historical documents and photos, and perhaps even sell souvenirs of the bunker—a West German equivalent to the East German wall in Berlin.

“There are not many concrete relics of the cold war left, aside from the wall,” Mausbach said. “I think it’s important to explain, especially to young people, what the cold war was about.”

Started in 1960, a year before the wall went up, the bunker cost $2.5 billion to construct. By the time it was completed in 1972, there were nearly 12 miles of tunnels, 936 bedrooms, 897 offices, and five small hospitals. It had five sections, each with its own electricity and water supply.

It was designed to enable 3,000 people to survive for 30 days after an attack. Among those, presumably, would be the chancellor, who could get here quickly from Bonn, the former West German capital, 18 miles away.

Ringed with barbed-wire fences and hidden among the leafy vines, it was—with apologies to the shadowy outposts lurking in the countryside around Washington, DC—the ultimate “undisclosed location”.

Just maintaining the bunker cost $14 million a year and required the work of 180 employees. Unable to defend its expensive dinosaur, the government decided in 1997 to abandon the complex.

Its first move was to solicit proposals from the private sector for other potential uses. The ideas—amusement park, a restaurant or a cultivation centre for mushrooms—seemed fanciful. So the government decided on Plan B: strip out the contents of the tunnels and seal them forever, returning the site to as close to a natural state as possible.

Mausbach began that work in 2001 but halted it for a few weeks after the September 11, 2001, terrorist attacks in the US while the government deliberated whether the bunker might have a use after all. “They concluded that a big bunker was not suited to this new kind of terror,” he said.