Derinkuyu
Meaning "deep well," Derinkuyu is the deepest of the known underground cities that have been explored. Eight floors are open to the public, though there may be many more. The subterranean labyrinth has stables, wineries, a chapel and baptismal pool, a school, scores of other interconnected rooms, and as many as 600 entrances and air ducts. You'll also see a ventilation shaft that plunges 180 feet from ground level. Claustrophobes, take note: spaces here are so tight that you'll have to walk doubled over for about 330 feet up and down steps in a sloping cave corridor.