Some flew over the barrier in hot-air balloons. Some sailed far around it across the Baltic Sea. Others sneaked across, hidden in secret compartments in cars.

And several hundred took advantage of the city's soft, sandy soil to tunnel beneath the Wall.

Today, Berlin's Cold War-era bunker-and-tunnel system has become one of the city's most popular attractions for tourists and local residents.

Last year, more than 150,000 visitors explored the underbelly of the German capital, touring the deserted bunkers and tunnels that are another reminder of the city's tense and violent role in the 20th century.

From the 1960s to the 1970s, Hasso Herschel helped dozens escape from the East to the West through the secret tunnels, some of which he dug with his own hands.

"This was the best thing I ever did in my whole life," the 74-year-old retiree says.

Herschel, who escaped to West Germany with a forged passport in 1961, escorts groups through the tunnels, explaining how the subterranean escape routes worked.

He dug his first illegal tunnel in September 1962. Its entrance was hidden in a house on the eastern side of the border, across from the wall on the Bernauer Strasse, says Herschel's sister, Anita Moeller, who helped him to cross.

"We went into the house, down to the basement, and then had to get into a hole in the floor," says Moeller, who escaped with her infant daughter and husband. "First I was worried, because I'm claustrophobic. I'm afraid of dark and narrow places . . . but once I was inside the tunnel, there was no time left for my fears."

Twenty-nine people fled through that shaft, making it one of the most successful tunnel projects at the time.

While some tunnels were less than 100 feet long, others were up to 557 feet. Some were like small tubes, barely large enough to crawl through, while others were large enough to stand up in. It took from three days to six months to dig the various tunnels between 1961 and 1982. About 300 people managed to escape through the tunnels.

Fleeing East Germany was dangerous. Border guards had orders to shoot any escapees on the spot. Researchers estimate that 136 people died trying to cross the Wall and that 700 to 800 perished along the 856-mile length of the border separating East and West Germany.

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 digging a tunnel by East German authorities on June 12, 1962. Noffke was killed and Hoetger was badly injured.

Tunnels often were discovered by border troops or the Stasi, East Germany's dreaded secret police, before they could be used. Others collapsed accidentally or were flooded by groundwater.

"Altogether we have counted 71 tunnel projects, and 20 percent of those were successful," says Dietmar Arnold, the head of the Berlin Underworlds Association, which conducts the tours and works on opening more underground 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 tells a tour group.

The tours usually start at a labyrinthine Cold War bunker in the bustling immigrant neighborhood of Wedding. The Underworlds Association has created an illustrative model tunnel, equipped with buckets, shovels, and a little wooden box wagon 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.

The groups move on to Bernauer Strasse in the Mitte neighborhood, one of the most popular spots for tunnel diggers because of the high amount of clay in the soil.

At least 15 attempts were made at Bernauer Strasse to burrow to freedom, Arnold says.

"Today, none of the original tunnels are still accessible, but sometimes, during street-construction work, unknown ones get discovered," he says.

In the first months after the erection of the Berlin Wall on Aug. 13, 1961, about 600 refugees fled through the city's canals and subway system. But by the end of the year, East German border troops had sealed off all access.

Then 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 recalls. "It took me a while to understand I was free . . . and only then I experienced this complete inner happiness."

Great Escapes

The Berlin Underworlds Association offers Tour M - Breaching the Berlin Wall, Subterranean Escapes from East Berlin to West Berlin - in English on Wednesdays at 1 p.m., April 1 to Oct. 31.

Tickets: About $17.75

for adults, $13 for children.

Location: Meet for the two-hour tour at the association's main office in the U8 Gesundbrunnen Station.

Web site:

www.berliner-unterwelten.de.