Tourists are flocking this spring to see surviving Nazi era bunkers in the German capital, with underground tours specially laid on for visitors fascinated by the city's bizarre network of underground shelters and tunnels.
This is in marked contrast to earlier post-World War II decades when the German authorities, perhaps understandably, preferred to remain silent about the more than 300 bunkers that had survived the grim, 12-year period of National Socialism.
During the city's cold-war division, communist East Berlin officials particularly turned a blind eye to the existence of buildings, bunkers and tunnels with a Nazi connotation.
For decades, citizens were kept in ignorance, for example, of the precise whereabouts of Hitler's bunker, where the "Fuehrer" committed suicide in early 1945 when the Russians arrived to seize the city.
A large hump in the "no-man's" land area of the Wall near Potsdamer Platz, caused when Soviet Army troops made a hash of blowing up the bunker in the late 1940s, was the only visible clue to its existence for years.
Not until last June did the Berlin Underworlds Association, a non- profit group founded 10 years ago, break a long held German taboo by erecting a shield pinpointing the notorious underground bunker site.
The Hitler bunker had been finally levelled in the 1980s, allowing a kindergarten to be built on the site of the Fuehrer hideout.
Nowadays, in addition to maintaining an underground history museum, the underworlds association arranges selected tours of remaining World War 11 bunkers and shelters in and around the city.
Close on 1,000 underground bunkers were built during the Nazi era to protect citizens. Many lay in ruins at the war's end after being targeted by allied bombers and Soviet artillery fire.
But almost a third survived, some virtually unscathed. Dietmar Arnold, the underworlds association co-founder, says for a long time the German authorities were nervous the "Fuehrerbunker," off the Wilhelmstrasse, might become a shrine for neo-Nazis.
It was similar thinking that led to Spandau Prison being torn down after the suicide of Hitler's deputy Rudolf Hess in 1987. Now a supermarket exists on the site.
But city attitudes have changed in recent years. Ingeborg Junge-Reyer, the city's senator for urban development today finds praise for the work of the underworlds organisation.
"Not many people know how Berlin looks underground. It is not accessible for the most part. But they do have an interest in the history of their city and like to take a look at the city's tunnels and vaults," she says.
One prime example of Nazi era bunker architecture is that found at the corner of Albrecht and Reinhardtstrasse, not far from the city's Deutsches Theater (theatre) in Berlin. Built by the Nazis in 1942, mainly as a refuge for 2,500 Reichsbahn (German railway) workers during bombing raids, its floors were divided into eight chambers.
By late 1944 more than 5,000 terrified Berliners sat huddled inside the metre-thick-walled premises, with its narrow window slits, as allied raids intensified.
Three years ago Christian Boros, a Wuppertal entrepreneur and art collector bought the listed bunker building for his family. Now it sports a luxury penthouse suite and garden, a swimming pool, and numerous art exhibition rooms.
Tempelhof Airport, one of the world's biggest building terminals, whose arc-shaped hangars were designed in the 1930s to resemble an eagle in flight, also possesses a huge web of underground bunkers, in addition to a Nazi-designed aircraft assembly line running four miles beneath the surface.
In the year 2000 a Nazi archive with files on 4,000 people forced into slave labour during the Third Reich was found in one of its bunkers. In 2008 the Berlin city government intends closing down the terminal that also is a state-protected building.
At the beginning of the 1970s, the then West Berlin authorities began refitting some of its underground bunkers as nuclear fallout shelters. One of the best known is that found at the Pankstrasse underground (U-Bahn station).
A steel door at the station leads to a bizarre underground concrete shelter worthy of a John Le Carre novel. Capable of housing thousands from nuclear attack, its storage rooms contain bunk beds, blankets, along with polyester jogging suits for 3,500 people.
The bunker, which forms a spaghetti network of underground shelters, is also equipped with wicker cradles and prams for infants and several stacks of body bags.
Curiously, a complex several stories in height beneath a skyscraper on the fashionable Kurfuerstendamm - also planned to house thousands in an emergency - today serves as a history museum during the day. And, rumour has it, as a party venue with a macabre attractiveness of its own at weekends.
Incidentally, of recent-year structures in the Berlin government quarter only the Chancellery building, three quarters of a mile from the Reichstag, has been equipped with underground shelters on two levels.
Wolfgang Schaeuble, Germany's Interior Minister, has no protective bunker in his glossy high-rise Ministry premises in the city's Moabit district. The owner, it seems, failed to consider such "extras" when the building was conceived in the early 1990s.
Now, rumour has it the government plans "new" 220-million-euro Interior Ministry premises in Moabit - presumably, with bunker included!