The Cult of the Dark One built a monastery inside the town. Only the cultists dare to enter it. It is a very deadly place because there are traps everywhere, including a guardian hectapod over the door which only allows cultists in, after they show the Dark One's Sign. Now that there are so few cultists left, none of them dare to enter the town because they are afraid the townspeople would overwhelm them. Although the monastery is empty, it is still feared by the townspeople.
It contains a hidden basement, with an altar to the Dark One Avoozl, the Mad Monk's desk with his notes on the rituals, and a Cask of the monastery's 'official' product, a wine which brings dark visions to the drinkers.
After the confrontation between Piotyr, Erana, their reinforcements, and the cult, the monastery stood empty for decades until someone discovered its secrets, got everything useful from it, and then set it on fire.