
Puerto Princesa Underground River —
Take a guided rafting trip to explore the five-mile-long Puerto Princesa Underground River in the Philippines.

Turda Salt Mines, Romania —
This former salt mine, excavated by hand since the 13th century, is now a museum and wellness and recreation center.

Thrihnukagigur Volcano, Iceland —
Visit in summer to explore this volcano, which last erupted 4,000 years ago.

Poço Encantado, Brazil —
The Poço Encantado (Enchanted Well) in Brazil is an underground lake with a window to the Bahian jungle above.

Cave of Crystals, Mexico —
Massive beams of selenite dwarf explorers in the Cave of Crystals.

Waitomo Glowworm Caves, New Zealand —
Take a boat ride to explore caves filled with New Zealand's indigenous glowworms. Their blue glow is caused by a chemical reaction in their abdomens.

Greenbrier Bunker, West Virginia —
The posh Greenbrier resort has a secret: a bunker built in 1956 to house members of Congress should nuclear war break out.

Santa Maria della Concezione dei Cappuccini, Rome —
Visit the Capuchin ossuary beneath the church of Santa Maria della Concezione, where the bones of 4,000 monks decorate the crypt.

Forestiere Underground Gardens, California —
A Sicilian immigrant built this subterranean home and garden modeled after the ancient catacombs of his homeland.

Cabinet War Rooms, London —
The Cabinet War Rooms -- part of the Churchill War Rooms museum -- preserves many day-to-day artifacts used by British leaders during World War II.



