Ruby Falls is the tallest and deepest underground waterfall open to the public in the United States. The 145-foot underground waterfall is located more than 1,120 feet beneath the surface of Lookout Mountain. The hugely popular tourist attraction offers guided tours daily.

Ruby Falls is a very small part of Lookout Mountain Cave, of which has a mapped length of 2.5 miles and has been closed to the public for decades. The natural cave entrance is at the base of Lookout Mtn. on U.S. 41, overlooking I-24 and the Tennessee River, but cannot be accessed by the public.