The Sunken Scriptorium

From the introduction:

The scriptorium was once the tower of a wizard who disappeared long ago. It was then briefly used as a military outpost, but as the territory became more settled it was sold to a sage who used it as a scriptorium, employing scribes to copy rare books. The tower’s foundations were undermined by the tunnels of purple worms, and eventually the whole edifice sank into the ground. Now it is a haunted ruin. Some quest item a book or statue is here.