From PathfinderWiki

Crystalrock is a large, natural cavern located in the Mindspin Mountains of south-eastern Varisia near the banks of the Falcon River.1 It was discovered by the dwarves of Janderhoff who also call it the "Heart of the World". Within the cavern is an enormous crystal formation which hangs suspended from crystal threads. Dwarven elders have gathered here annually for centuries to watch the formation shake and give off a low pulse which can be felt for miles around. Lately the "heartbeat" has been occurring more rapidly, a fact which has caused the dwarves much concern; at the moment, it is aligned to the changes of the seasons.234

The cavern also gave its name to the Treaty of Crystalrock, signed here in 4472 AR between Janderhoff and the nearby Chelish city of Korvosa.5