This cave is shown during the day, when the moonlight is the weakest. The cavern is generally abandoned, most do not visit due to the dangers of collapsing. This cavern does indeed lead to an opening on the other side of the large mountain.
This waterfall is situated behind the camp, inside one of many caverns. One is able to hear the gushing waters that flow through. Without the moon's power to cause waves, the waterfall is lighter in volume, revealing a cave hidden behind.