The United States' most epic waterfall (1100 feet underground)

The US is full of incredible offbeat waterfalls, like the shockingly blue Havasu Falls, the massive Niagara Falls, the enchanting beach-side McWay Falls or the lush green tiers of Multnomah Falls, but there's nothing that can really compare to the size and secrecy of Tennessee's Ruby Falls. Deep inside the heart of Chattanooga's Lookout Mountain, you'll find one of America's tallest and most incredible natural features. A hike through the mountain's cave system takes you right to the base of the 145 foot waterfall, which is believed to be the result of 30 million years of erosion through the limestone rock. Water from rain and natural springs gathered and worked their way through the mountain's core to form the falls, which collect at the base and wind their way through and out of Lookout Mountain to join the Tennessee River.

The waterfall remained a hidden secret locked within the moutain until the late 20th century. Few people entered the cave system and the natural entrance was closed to build a railway tunnel. It wasn't until the 1920s when a local spelunker named Leo Lambert decided to open up the caves again and raised money to drill into the mountain. By 1928, he was ready to begin cutting in. As he and his team dug further in, and did some exploring through the natural cave system, they eventually discovered the magnificent falls. Leo decided to name them after his lovely wife Ruby (cue the awwws). It proved to be a popular tourist attraction; it was one of the first caves to have electric lights, and an elevator was eventually put in as well.

Fun fact: although the water is totally pure and safe to drink, it picks up large amounts of magnesium (it's a natural laxative!) as it flows through the cave so it's really not enouraged. Also, Johnny Cash and Roy Orbison co-wrote a song called "See Ruby Fall" inspired by the ubitquitous ads for the attraction plasted on barns and billboards across Tennessee and beyond. Sure, the ads are cheesy, but you have to admit...a waterfall inside a mountain is kind of awsome.