Gnome forest

The crystal caves are a group of caves found within the Gravity Falls forest that are home to the gnomes.

Appearance
The caves are accessed through the forest via a steep slope. They are filled with countless glowing crystals, as their name implies, and also contain various plants, predominantly trees, and moss fungi, notably mushrooms. Stones and puddles can be seen on the ground, which has various levels and is largely covered by grass.

History
In "Tourist Trapped," after the gnomes, who had disguised themselves as a teenage boy named "Norman," reveal their true identity to Mabel Pines, they feel the need to kidnap her and take her back to the caves when she states that she cannot date a group of gnomes. Soon Dipper Pines, believing "Norman" to be a zombie, comes to his sister's aid and frees her from the gnomes' clutches, and the two head home in the Mystery Cart. The gnomes, however, wish to retrieve Mabel and crown her as their queen, assemble into a single, giant monster and chase the twins. The caves later appear in the end credits. They also serve as the fourth level in the game "Fright Night."