Trembley's Cove

The underground cave is a hidden location underneath the Gravity Falls Cemetery, accessible by pulling down on the finger of an angel statue. It contains many historical artifacts, specifically documents, like one showing Abraham Lincoln had a hand on his head and that's why he wore his hat, and one showing that Benjamin Franklin was a woman.

History
In "Irrational Treasure," Dipper and Mabel Pines set out to uncover the truth as to whether or not Nathaniel Northwest was the true founder of Gravity Falls, Oregon. After following a series of clues, the twins find the cave that was triggered by a statue's finger, thanks to Mabel pretending an angel statue is picking her nose. The two descend a set of stairs they unearth and, in an underground corridor, accidentally set off a trap that shoots tranquilizer darts at them; they quickly run through and make it to the end of the main part of the cave unharmed. There, they find many historical documents on historical secrets, including the one they are searching for, the Northwest cover-up, as well as other artifacts. They read the document and learn the identity of the real founder of Gravity Falls: Quentin Trembley.

Soon, Sheriff Blubs and Deputy Durland arrive, finding their way by following Mabel's trail of candy wrappers, and confront the twins. However, they are delayed by Durland fainting, due to being hit with an excessive amount of darts. After Durland comes to, he and his associate show Dipper and Mabel a film regarding Trembley, showing how he won the election in a literal landslide and did such a great number of silly and "shameful" acts that he was removed from office. Then, the film shows him fleeing to an uncharted valley which he named "Gravity Falls" after plummeting into it at high speed. The documentary then ends, and Sheriff Blubs shows the twins Trembley's body encased in a block of solid peanut brittle. Blubs and Durland then ship the twins, Trembley and the artifacts to Washington, D.C.

The cave makes a brief cameo when Bill Cipher is mentions knowing "lots of things." Namely famous conspiracies.