The Mad Abbot's Lair

From the introduction:

Abbot Van-Wolff, ever experimenting with the dark arts, has triggered a devastating Portal mishap. An explosion of energy has vanished an entire segment of the underground temple leaving a bottomless pit. Worse, the portaled earth and stone has reappeared over the main abbey destroying the structure with its sudden violence. Locals have attempted several rescue missions but few return. Those that do report of walking undead, Monsters and the echoing laughter of the Mad Abbot!