Megadungeons - Archlich's Lair

Publisher's blurb:

During his life the evil wizard Xayomm dreamed to become a powerful archlich. He studied for decades through research and experiments while hiding in his lair, next to a small mining town. A group of brave adventurers discovered his plans and fought him in the dungeon. Unfortunately it was too late. Xayomm defeated the party and turned into a mighty undead. Then, his undead minions stormed the town killing all the poor miners and seizing the whole area as Xayomm domain. Today, the town is a ghost town and no one dares to enter the Archlich's Lair.