Witch of the Demon Seas - Poul William Anderson

"Guide a black galleon to the lost, fear-hauntedCitadel of the Xanthi wizards—into the very jaws of Doom? Corun, condemned pirate of Conahur, laughed. Aye, he'd do it, and gladly.It would mean a reprieve from the headsman's axe—a few more precious moments of life and love ... though his lover be a witch!" Publisher blurb - Summary by Publisher