BERLIN -- The Gesundbrunnen subway station in north Berlin leads out to a shopping mall and a park, connects to a street car and a few buses, and has probably tens of thousands of people walking up and down its stairwells every day.
Few of them probably ever see the pale green door that blends so seamlessly into the swimming-pool-tile facade the station's designers selected in a moment of poor taste.
Then Thomas Breuer arrives with a gaggle of people following him, unlocks the door, and steps inside. A few commuters turn to look, but catch only a glimpse of a musty passageway. Then the door closes as Breuer and his group disappear into the darkness to explore one of the last vestiges of the city's subterranean Nazi legacy.
Breuer, a professional tour guide, is a member of the Berlin Underground Association, the only organized group documenting the bunkers built by Hitler and his cohorts during World War II to protect them from Allied bombs. For the past four years, the group's tours through two bunkers in the north of the city have drawn visitors from Tokyo to New York at an ever-growing rate. Last year, 17,000 paid the 9 euro fee (about $11.25) to walk the narrow, concrete passageways.
''Many people who've already seen the Brandenburg Gate want to see the city from another side," said Dietmar Arnold, the organization's head, who started clambering around old Nazi ruins as a child in West Berlin. ''They want to see the guts of the city, and see what it looks like from below."
The bunkers don't have the polished look of a slick museum exhibition or the imposing gravitas of the remnants of Hitler's Olympic stadium. The attraction here lies in the very fact that little has changed since the days when women and children cowered in the small passageways. The ghosts of the Third Reich, in Germanic writing on the wall or the stack of hospital beds in one room, are ever-present in the bunkers. Display cases filled with encrusted rifles or helmets pocked with bullet holes bring home the deadly toll of war.
The group's biggest discovery so far in its burrowing around Berlin has been a large, block-sized information storage system with the names and addresses of thousands of forced laborers during the Nazi regime, a discovery that led to compensation for some of the survivors. It serves as the highlight of the Saturday tours Arnold and his group lead.
As a child, Arnold dodged the police while digging up old medical supplies or helmets around the ruins of Nazi buildings yet to be cleared away by the West German government. After the fall of the Berlin Wall, he received permission from the city to explore the old bunkers.
In 1997, Arnold and his partner, photographer Frieder Salm, published a book, ''Dark Worlds," and founded the association. Two years later, the group led its first organized tour. In 2004, they plan to open a five-level bunker beneath a nearby artillery tower that Arnold said will be ''magnificent."
The current 90-minute tour through two bunkers begins at the bottom of three flights of stairs. There Breuer begins with a little history.
As British bombers made bolder forays into Germany during the war, the Nazi leadership made plans for massive underground bunkers to house, well, mostly themselves. Field Marshall Hermann Gring built the first bunker underneath his air force ministry. Bunkers followed for Hitler, Goebbels, their drivers, and more.
Grand plans were made to build bunkers that would house about 10 percent of the Berlin population. By the end of the European war in May 1945, the 1,200 bunkers built were enough to hold only 3 percent, or 26,000 people.
''You could see how interested they were in protecting their people," Breuer said.
The tour leads through an irregular maze of concrete rooms with low ceilings. On the wall, the association has hung signs documenting the effect the postwar division of Berlin by the Allied powers had on the underground. Photos show the rerouting of canals and water pipes so that nothing connected East and West Berlin below the streets.
The tour winds through room after room rather quickly and visitors get a good idea of the confusion that reigned as the end came.
''The uncertainty, that was the worst for the people," said Breuer. ''Some said it was worse to be here than on the front, because there you at least knew what was going on."
Many bunkers -- including Hitler's storied Fuehrerbunker near the center of Berlin, the Potsdamer Platz -- were damaged beyond use. Allied forces welded most of the others shut, or detonated entry passages, making them inaccessible.
During the Cold War and under the threat of nuclear attack, politicians in West Berlin looked at the bunkers with renewed interest. About 41 were considered renovation- and expansion-worthy by the government in 1967, said Hans-Joachim Beuke, a bunker expert in Berlin's planning department.
But maintaining them cost tens of thousands of dollars a year and got less interesting in 1990.
''Before Sept. 11 they were ready to completely abandon the bunkers," Beuke said. The terrorist attacks changed attitudes, and Beuke's department got its planned 80,000 euro budget (about $100,000) approved without the fuss of the preceding years. But bunkers built for a conventional war are not much use in the age of bunker-busting bombs and when the deadliest weapons can come in the mail. Even Beuke admits they are little more than ''sedatives."
The old Nazi bunkers don't even rate that high. Fears that the bunkers could turn into neo-Nazi shrines have meant Berlin politicians prefer to close them. ''There was concern [neo-Nazis] were going to use them to meet," said Beuke.
Underground activists scoff at the argument, and say the government is in denial. The bunkers tell an important story, said Arnold, and one not covered in German history classes that place heavy emphasis on the Holocaust and Nazi blitzkrieg, but soft-pedal the suffering of ordinary Germans at the expense of the Nazi regime's actions.
In order to ensure the next generation gets the message, the association brings in war survivors to talk to school groups at organized seminars. The seminars are not yet available in English, but judging by the reaction Arnold has gotten to his underground tales when he has traveled to the United States, they soon will be.
On a recent trip, suspicious US Customs agents pulled him out of the line at New York's JFK Airport. After rooting around in his bag and discovering his book, they asked Arnold to explain. The Berliner captivated an audience of seven officers for more than an hour with tales of the Nazi underground. At the end of it, he got a full escort out of the airport.
''I was shocked at how interested they were," Arnold said. ''They were more interested at times than the people here."
Andreas Tzortzis is a writer in Berlin.