Ruby Falls, USA

Ruby Falls is a 145-foot high underground waterfall located within Lookout Mountain, near Chattanooga, Tennessee in the United States. Ruby Falls Cave features many of the more well-known types of cave formations  including stalactites and stalagmites, columns, drapery, and flowstone. The Falls are located at the end of the main passage of Ruby Falls Cave, in a large vertical shaft. The stream, 1120 feet underground, is fed both by rainwater and natural springs.  Source