In this brief, indispensable guide, Irwin introduces the stunning Moorish palace and fortress complex, revealing its mysteries, myths and significance with wit and insight. He opens with a romantic description of the fairytale structure, which he then deliciously demolishes. Includes a detailed floor plan, sketches and aerial photographs. A volume in the Harvard University Press series, Wonders of the World. Irwin is a British novelist and Islamic scholar.  (SPN226, $14.95)