The Cave Key is a key item that appears in Super Paper Mario.
During the events of Chapter 5-3, Mario and the heroes ran into Flint Cragley near a locked door. However, Flint himself says he gave the key to one of his two crewmen and that the heroes must find them for Flint in order to get the key. However, it later turns out Flint himself had the Cave Key and unlocks the door which leads to the end of the level. Later on, another Cave Key can be found and it leads to the Pixl, Dottie.