Crystal Dimension is a place where Tree Trunks went and ruled after she ate the Crystal Gem Apple. It first appears in the episode "Tree Trunks" at the end of the episode. Its major appearance is in "Crystals Have Power" as a place where Finn is turned into a crystal person. It is also the place where the Rainicorn-Dog wars happened. It is said that Rainicorns live in the Crystal Dimension in the episode "Her Parents."
It is a place that is very vast. It is made out of multicolored crystals, varying to colors from pink to purple to red mainly. This world looks like a large crystal mine.