The Underground Cave is located under the edge of the Grass Lands. The entrance to the cave is a large, deep hole in Banana Man's backyard.
The Underground Cave is dark and damp. There is a huge, deep lake in the cave. Stalactites hang from the ceiling and stalagtites grow on the floor. The land in the cave has a grayish-purple color. Stalagmites formed easily due to the cave's dampness.
They are the same color of gray-purple as the land around them. They range in size from very tiny to bigger than Finn. The cave's main feature is its lake. The lake is so deep and dark that is resembles outer space. Banana Man's rocket sunk into the lake. In Jake's Croak Dream, Jake drowned in the lake, but it was Finn who really almost drowned in the lake.
