From PathfinderWiki

Created over 200 years ago by the necromancer Volzaras, an exile from Geb, Bonekeep refers more specifically to the heavily warded dungeon beneath the ruined siege fortress. The white stone fortress is close to the city of Absalom and shortly after construction was the launching point for the necromancer's siege of Absalom by his undead forces. The castle has lain dormant for centuries after being razed in Absalom's response action. More recently, it has been the subject of several Pathfinder Society expeditions after the previously unknown subterranean levels were discovered.123