Ruby Falls, located deep within Lookout Mountain near Chattanooga, Tennessee, is recognized as the tallest and deepest underground waterfall open to the public in the United States. It features a spectacular 145-foot (44-meter) drop into a limestone cavern located approximately 1,120 feet below the mountain's surface. Discovered accidentally in 1928 by Leo Lambert (who named it after his wife, Ruby), the waterfall is fed by both natural rainwater and underground springs, eventually flowing into the Tennessee River. In 2026, visitors reach the falls via a high-speed glass-fronted elevator that descends 26 stories into the earth. The "Falls Room" utilizes a state-of-the-art synchronized LED light and sound show to highlight the water's descent, which has been a staple of American road-trip tourism for nearly a century. While there may be larger "wild" underground waterfalls in inaccessible cave systems, Ruby Falls remains the largest and most significant subterranean cataract accessible to the general public, maintaining its status as a National Historic Landmark in 2026.
The largest and most famous underground waterfall in the United States is Ruby Falls, located deep within Lookout Mountain near Chattanooga, Tennessee. This stunning 145-foot (44-meter) waterfall is situated over 1,120 feet below the surface. In 2026, it remains a premier geological attraction, where visitors take a glass-front elevator down 260 feet into the cavern before walking through a trail of stalactites and stalagmites to reach the thundering falls. The waterfall is illuminated with a multi-colored LED light show, creating a dramatic atmosphere. While there are other subterranean falls in the US, Ruby Falls is the tallest and deepest that is open for public tours, making it a "must-see" for nature enthusiasts exploring the American South.