Discovered in 1927 by a woodcutter who literally stumbled into them, these limestone caverns have fascinated visitors ever since. Tours range from the wheelchair-accessible Short Tour ($16, 30 minutes) to the Explorers Tour ($80, 2½ hours), and the Wild Tour ($99, 2½ hours), which picks up where the Explorer finishes and delves into caverns only recently discovered. Note that young children aren't permitted on the Explorers or Wild tours.
The owners now also run one- and two-day motorized rafting trips down the last 70 miles of the Grand Canyon. Prices start at $800; see www.grandcanyon9rapids.com for details.