Ruby Falls is a 44 meter (145 ft.) high underground waterfall located about 341 meters (1120 ft.) below the top of Lookout Mountain, near Rock City and Chattanooga, Tennessee, USA. This surprising waterfall comes from the roof inside a cave created with the formation of Lookout Mountain, about 200 to 240 million years ago. The stream, fed both by rainwater and natural springs, is collected in a pool in the cave floor and then continues through the mountain until finally join the Tennessee River at the base of Lookout Mountain. Electric lights were installed in the cave to turn it attractive colored.
The Lookout Mountain Caverns, which includes Ruby Falls Cave, is a limestone cave, which occurs when slightly acidic groundwater enters subterranean streams and eats away the soluble limestone, causing narrow cracks to widen into passages and caves in a process called chemical weathering.