Cave Dungeon

Cave Dungeon is the name of a potentially unused course from Super Mario 64's development, only evidenced by the source code and Original Soundtrack.

Evidence
Unused Level 38, referred to internally as "sm64/map/stage38/sand.sou", is an unused map that tests multiple in-game mechanics. The mechanics include the teleportation spots, the reflection of the Mirror Room, and the sand in Shifting Sand Land. Based on an unused dynamic audio file named "(scn_msc_cavdg)" in the source code, the slot for this level originally belonged to a stage called Cave Dungeon. Interestingly, the name Cave Dungeon also appears in the official soundtrack album, where it is the music used within stages like Hazy Maze Cave and Wet Dry World. It is unknown if Cave Dungeon has ever been recreated by the AI, although it is unlikely as the name is the only remnant of the stage.