I finally got around to reading this paperback that's been sitting in a stack of books for maybe 20 years or more. It's sword-and-sorcery adventure by Andrew J. Offutt, published in 1976, and based on a character created by Robert E. Howard, best known as the creator of Conan the Barbarian. The character in this book is Cormac MacArt, a wild Irish Viking-type pirate of the late 5th Century, the time when the Western Roman Empire had collapsed. This is the 6th in a series about Cormac and in this one the wild Celtic raider leads a crew, including a gorgeous red-haired Irish warrior-princess, to an island that has an ancient and gigantic castle. Cormac believes it was built by his ancestor, King Kull, a mighty warrior who was from Atlantis ( another REH character) and that the castle also contains a treasure (of course). All standard sword-and-sorcery stuff, including "the undying wizard" of the title living on the island-- a villain who had been Kull's mortal enemy and would make himself Cormac's enemy as well. I give it a solid 3 stars, especially as this book took me back in time to the 70s when I passed many enjoyable hours reading the Conan paperbacks and other fantasy tales. Those were the days....