The Waterfall Cave is a location from The Legend of Zelda: Skyward Sword. Located in Skyloft, it is a small cavernous tunnel located behind the waterfall on the northwestern part of the island, hence its name. It leads to a small area on the underside of the floating island.
When searching for his missing Crimson Loftwing, Link eventually has a vision of his Loftwing under imprisonment. Using the Practice Sword given to him by Knight Commander Eagus, Link is able to destroy the trees blocking the entrance to the Waterfall Cave, and ventures inside. Inside the Waterfall Cave has many Keese and Green ChuChus. When Link makes it to the underside of the island, Link destroys the wooden boards used to imprison his Crimson Loftwing and is reunited with his companion.
After Link unlocks Skyloft's Silent Realm, a group of Blessed Butterflies can be found inside the cave at night. If Link plays the Goddess's Harp near them, the Moonlight Merchant will appear and offer to sell Link various treasures.