An Ancient Altar is a solemn chamber where you can make offerings to mysterious forces.
Empower: Purge Haunted Facility
You commission your hireling to lead a ritual that takes 7 days, during which time you must remain in the Bastion. At the end of the ritual, you must offer a worthy sacrifice, which can be monetary (1,000 GP) or blood (the fresh corpse of at least one Large creature or four Medium creatures that aren't Constructs or Undead). If you make a blood sacrifice, roll on the Bastion Hauntings table. Once the ritual is complete, the sacrifice is destroyed. Choose a Haunted special facility in this Bastion or in a Bastion connected to this one; that facility is no longer Haunted.
Blasphemous Charm
After spending a Long Rest in your Ancient Altar, you gain a magical Charm that lasts for 7 days or until you use it.