Ruby Falls is named one of the Ten Most Incredible Cave Waterfalls on Earth. It is America’s deepest commercial cave and largest underground waterfall. Enjoy a guided tour through the fascinating cavern with its unique rock formations. The highlight of the tour is the sparkling 145-foot underground waterfall.  It’s always fifty nine degrees inside of naturally wonderful Ruby Falls. See the panoramic view from the Lookout Mountain Tower. While on site, check out the new Ruby Falls ZIPstream Aerial Adventure – open seasonally.