Cascade Cavern - Watkins Glen, NY USA
As you walk up into Watkins Glen this is the second major waterfall you encounter (after the one by the entrance). The path takes you behind the falls and up the stairs to the right through a tunnel to the next level up. This spot is almost always packed during the day, but if you go in rainy weather, early in the morning, or later in the afternoon you can avoid having quite as much company. Anyway most people don't ever make it past this point - the come, see this waterfall, and then walk back down. My advice - Don't be that person!!! Some of the best views, including the iconic Rainbow Falls are farther up the trail!