The Goblin Tower — L. Sprague de Camp

King Jorian was rather attached to his head. Hence, he felt his promise to seal the Kist of Avlen, a treasure trove of ancient manuscripts on magic, was little enough a price to pay for a chance to escape his own beheading. But when the quest pitted him against one peril after another—a murderous wizard and his giant squirrel, a castle full of executioners, a marauding troop of ape men, and a voluptuous 500-year-old princess who was also a serpent—Jorian wondered if he''d made a good bargain!