Ruby Falls is a 145 foot tall subterranean waterfall located inside Lookout Mountain near Chattanooga, Tennessee.
It most certainly qualifies as what I would call a tourist trap. Tons of visitors line up to take a tour of the cave with the highlight being a chance to see the falls in person. It's actually quite entertaining and the caves are fascinating.
There is a lot of history behind the caves and public tours have been given since 1930.
Ruby Falls is certainly a stop to consider if you're ever in the area and find yourself with extra time on your hands.