What in the World

The tunnels and caverns, 22 miles of them, that riddle the ground beneath the London suburb of Bromley have been many things: arsenal, bomb shelter, concert site, film set, mushroom farm, supposedly haunted tourist attraction, and once even a makeshift maternity ward.

But there’s one thing the Chislehurst Caves have never been: caves.

The rough-walled tunnels were not naturally formed. They are entirely hand-dug: mined for chalk and flint for centuries, and put to use for almost anything requiring a cool, dark place. During World War I, munitions for the Woolwich Arsenal were stashed there.

During the Blitz, the caverns were transformed into an enormous air-raid shelter that could hold 15,000 people, complete with an underground hospital, chapel, barber, canteen and shops. A baby girl born in the shelter in 1941 was given the middle name Cavena.

“In 1944, when the V-1 rockets were coming, we had a mass influx,” said Jason Desporte, the general manager of Chislehurst Caves, where guided tours are offered daily from an entrance tucked away on a side street.

As with natural caves, the air temperature in the tunnels normally stays at a rock-steady 50 degrees Fahrenheit the year around. But the crowding during the Blitz warmed the tunnels to more than 70 degrees, and they took a year and a half to cool down again after the war, Mr. Desporte said.

In the 1960s, they became an offbeat performance hall for artists like the Rolling Stones, Jimi Hendrix, the Kinks, Pink Floyd and the Who. Led Zeppelin held a record-label launch party there on Halloween in 1974, a fittingly spooky date for a place rumored to be rife with paranormal activity.

The tunnels have also provided atmospheric settings for movies, music videos and television shows, including “Doctor Who” and “Merlin,” and for an immersive role-playing game called Labyrinthe.

For decades after the war, the management offered a prize of 5 pounds (about $7 today) for anyone brave enough to spend the night in the tunnels. Only one person ever won it — a police officer named Tony Bayfield in 1958. The offer was discontinued in 1985 for safety reasons after one hopeful dislocated his shoulder in the total darkness.

Correction: June 8, 2016

Because of an editing error, an earlier version of this article misspelled the surname of the general manager of Chislehurst Caves in one passage. He is Jason Desporte, not Deporte.