Puerto Princesa Underground River — Take a guided rafting trip to explore the five-mile-long Puerto Princesa Underground River in the Philippines. Simon Grosset/Alamy Turda Salt Mines, Romania — This former salt mine, excavated by hand since the 13th century, is now a museum and wellness and recreation center. http://www.flickr.com/photos/bogdanflo Thrihnukagigur Volcano, Iceland — Visit in summer to explore this volcano, which last erupted 4,000 years ago. Peter Roach Poço Encantado, Brazil — The Poço Encantado (Enchanted Well) in Brazil is an underground lake with a window to the Bahian jungle above. StockBrazil/Ala Cave of Crystals, Mexico — Massive beams of selenite dwarf explorers in the Cave of Crystals. Carsten Peter/Speleoresearch & Films/National Geographic/Getty Images 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. Courtesy of Spellbound Glowworm Cav 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. Ian Patrick/Alamy 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. Grand Tour Collection Forestiere Underground Gardens, California — A Sicilian immigrant built this subterranean home and garden modeled after the ancient catacombs of his homeland. http://www.flickr.com/photos/flyfarther79 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. Kevin Nicholson/Alamy Prev Next
