Dungeon of the Mad Mage

According to legend, in a time when there were still 9 gods instead of 7, a powerfull mage ruled the Dutchy of Ruhrheim . Untill one day their castle was swallowed by the ground. And their name lost to obscurity.
Recently an old gate was discovered after a landslide took place on the edge of Hogenterp. As some curious farmers cleared the rubble a withering man came walking out from the gate. He spoke in a shrill tone: "Save my kingdom from the mad mage, and it will be yours." He then crumbled into pieces, his ashes spreading with the wind.
Ever since adventurers known as Delvers have traveled to Hogenterp. In search of becoming wealthy by looting the riches of the dungeon.