This is the hideout of an evil cult. It's part of a larger complex of chambers and tunnels under a cemetery. Some of the locations were intended to be mausoleums actually.
The cult worships an occult entity from the void they only know as the "Black Star", but the high priests know better. It is a thing called an Atropus. It is believed to be the remains of a stillborn god, then resuscitated with evil necromancy. The cult's endgame goal is to redirect the course of the Atropus orbit so that it collides with the material plane. You know... basic cult stuff.
Pledge today and find out what it's all about.