It is not clear how many were killed trying to flee through the tunnel system. Last month, the city honored Siegfried Noffke and Dieter Hoetger, who were caught by East German authorities on June 12, 1962, while digging a tunnel. Noffke was killed and Hoetger survived but was badly injured.
Often tunnels were discovered by the border troops or the Stasi, East Germany's dreaded secret police, before they could be used. Others collapsed accidentally, were flooded by ground water or buried by loose soil.
"Altogether we have counted 71 tunnel projects and 20 percent of those were successful," said Dietmar Arnold, the head of the Berlin Underworlds Association, which conducts the tours and works on opening more subterranean structures to the public.
"Most tunnels were dug from the West to the East, often by men who had already fled to the West and who were now trying to get the rest of their family out of East Germany," Arnold told visitors during a recent tour of the tunnels.
The tours usually start at a labyrinthine Cold War bunker in the bustling immigrant neighborhood of Wedding. Here, the Underworlds Association has created an illustrative model tunnel equipped with buckets, shovels and a little wooden box wagon that was used to carry out the excavated soil. The light in the bunker is dim and fluorescent paint from the Cold War-era glows on the walls, creating an eerie atmosphere.
Later on, the groups move on to Bernauer Strasse in Mitte neighborhood, one of the most popular spots for tunnel diggers at the time, due the high amount of clay in the soil.
At least 15 attempts were made at Bernauer Strasse to dig a path to freedom through the soil, according to Arnold.
"Today none of the original tunnels are still accessible, but sometimes, during street construction work, unknown ones get discovered," Arnold said.
In the first months after the erection of the Berlin Wall on Aug. 13, 1961, about 600 refugees ran away through the city's canals and the subway system, but by the end of 1961, East German border troops had sealed off access completely.
It was then, that people started digging their way to freedom.
"We crawled on all fours through the mud, until we reached a ladder that we climbed up," Anita Moeller remembered. "It took me a while to understand I was free ... and only then I experienced this complete inner happiness."
___
If You Go...
TOURS OF BERLIN'S ESCAPE TUNNELS: http://www.berliner-unterwelten.de or 011-49-30-499-105-17. Tour "M" offered in English on Wednesdays at 1 p.m. through the end of October, and in German on Saturdays and Sundays at 11 a.m. Adults, $17.75 (12 euros); youth, $13 (9 euros).