The Alhambra, a Moorish fortress since the first Nasrid sultan, is built upon ancient Roman ruins and is a UNESCO World Heritage site. The "red castle" fell during the Rconquista in 1492 whereupon it became a royal residence.
The Alhambra complex consists of four groups of buildings, the Alcazaba (fortress), Nasrid Palaces (Sultans Residences), Palace of Charles V & Generalife (Gardens)