Marceline's cave is a cave in Ooo inhabited by Marceline and her zombie poodle, Schwabl. The cave's entrance appears in the opening title sequence. It has also appeared in "Evicted!", "It Came from the Nightosphere", "Go With Me", and "Heat Signature". The cave also appears as a level in Righteous Quest and Righteous Quest 2.
Marceline's cave has the appearance one would expect from a cave: a dark, dank open area with stalagmites, stalactites, and various other rock formations. Marceline's house is inside the cave, and features a large porch overlooking a lagoon. One of the cave's entrances is under an old, pre-Mushroom War highway bearing a rock face that greatly resembles a vampire.