Guimond's Tower and the Lair of the Druid-Lich

From publisher blurb: An abandoned forest tower haunted by the undead and twisted 'caretaker' of the local forest. A druid, cast out and transformed into an undead horror, has mutated the local wildlife and forest into a tragic parody of its healthy self. Built using Swords & Wizardry for a high-level party to purge the forest of its corrupted guardian...