Subterranean

A subterranean world of tunnels links several buildings of this rare 19th-century asylum.

This centuries-old mine remained hidden beneath a hotel bar until 2013.

The only subterranean ping pong table in Atlanta.

A sixth-century Byzantine cistern hidden below a modern carpet store.

A Roman spa buried deep beneath the City of London.

This small museum tucked within a subway station holds pieces from Madrid's past.

A more than 260-year-old crypt built on Boston's oldest English burial ground.

Its dark depths conceal millions of rare, delicate crystal formations.

The remains of an Aztec school and various intriguing artifacts lie below a modern cultural center.

This army of concretions is an unexplained geological phenomenon unlike anything else in the world.

This Roman quarry once held secret masses and smuggler's contraband and is now home to rare species of bats.

There's a labyrinth of manmade tunnels stretching for over an acre beneath Bristol.

Hidden in a grotto 26 feet below Nottingham's oldest hotel, this stylish subterranean drinking den is notoriously hard to find.

There's a labyrinth of medieval chambers hidden deep below a 15th-century pub.

Long tunnels run under the ancient chariot racing circuit to the tower.

The world’s largest underground marble quarry is hiding in Vermont.