The compleat enchanter

The Harold Shea stories are parallel world tales in which magic exists in separate universes which coexist with our own, and which can be reached by aligning one's mind to them by a system of symbolic logic. The worlds frequently are based on the mythologies, legends, and literary fantasies of our world. In the stories collected as The Incomplete Enchanter, the authors' protagonist Harold Shea visits two such worlds, that of Norse mythology and that of Edmund Spenser's The Faerie Queene. (From Wikipedia) Grab your Syllogismobile and join Harold Shea as he copes with evil wizards, fantastic beasts, and not entirely successful magic. Light-hearted fantasy in the grand tradition.