The Worm Ouroboros

A novel of high fantasy and spellbinding imagination set on the (strangely earthlike) planet Mercury and peopled by Ghouls, Goblins, Imps, Demons, and Witches, The Worm Ouroboros tells the epic tale of the conflict between Witchland and Demonland, including an heroic quest to free Goldry Bluszco, banished by sorcery to a remote mountain peak for the killing of Witch-King Gorice XI.
Written in sweeping, heroic, saga-like prose and shot through with stirring poetry, Ouroboros greatly influenced the work of both J. R. R. Tolkien and C. S. Lewis, predating Lord of the Rings and Chronicles of Narnia by some 30 years. Tolkien was especially impressed by the book, declaring its author to be "The greatest and most convincing writer of invented worlds that I have read."