Pan's cave is the cave where the god Pan hid and faded. Pan's cave is located in Carlsbad Caverns, New Mexico. The fact that Pan hid in a cave was the reason satyrs never met him, since none would go underground.
The cave and Pan were eventually discovered near death by the satyr Grover Underwood and his friends: Percy Jackson, Annabeth Chase, Nico di Angelo, Rachel Elizabeth Dare, and Tyson. Pan resided in this cave because it was one of the few truly wild places left on Earth, but it too would eventually be cultivated by humans. There were extinct animals, and Percy says, "There was a dodo bird, something that looked like a cross between a wolf and a tiger, a huge rodent like the mother of all guinea pigs, and roaming behind the bed, picking berries with its trunk, was a woolly mammoth."
Pan also passed on words of wisdom and advice to every member of this party, besides for Nico. He also gave Grover the appointment to preserve the wild, the power of causing massive panic, and the duty of telling the other saytrs of his death which resulted in Grover's exile.