The Cappadocian Tunnels

The Cappadocia region in central Turkey is well-known for its surreal scenery with fairy chimneys and cave houses. The ancient underground towns etched into the pliable volcanic rock, however, are even more fascinating.

The biggest of these cities, Derinkuyu, could accommodate up to 20,000 people and had everything from stables to kitchens and places of worship. These subterranean structures functioned as havens in times of conflict and invasion.

The Dragon's Breath Cave

Located in Namibia, Dragon's Breath Cave is home to the world's largest underground lake. This hidden 2.5-acre aquatic expanse was found in the 1980s, but because of its difficult access and distant position, it has not been thoroughly examined. The humid air that rises from the cave's entrance and resembles a dragon's breath is what gave rise to the cave's name.