Subterranean

A former copper mine which became a truly unsuccessful prison.

Semi-precious Blue John stones have been mined in this cavern system for centuries.

This massive subterranean fissure is known as the "underground Grand Canyon."

Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

One of the largest underground systems runs under Canada's largest urban center.

This underground power plant looks more like a super-villian's lair than a public work.

A subterranean house of worship carved right out of the bedrock.

The deepest metro station in the world.

Beneath the city of Lourdes, France is a massive, concrete church.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

The odd cement nubs littering this Spanish square are actually the entrances to a series of buried silos.

The United States's largest hand-dug well is topped with a state-of-the-art museum.

A hyper-luxurious, 12,000- square foot home might be buried beneath Queens, still waiting to protect you from nuclear missiles.

The former locus of Boston's high culture has been shuttered and buried for over 70 years.

The world's largest man-made underground caverns offer unparalleled underwater wonders.

This long, dark tunnel is open to hikers, but those without lights are known to get confused even on the straight path.

This series of Scottish caves has no clear purpose other than baffling historians.