Built in the 8th century as a caliphate residence on the site of a Visigoth fortress, the Alcazar was used as the residence and fortress of Ferdinand and Isabella (the "Christian Monarchs" for whom the building is now named) as well as a headquarters for the Spanish Inquisition. The fortress, with its artifacts (including a series of Roman mosaics and a Roman sarcophagus) and two towers is now open for touring, but the main attraction here is the lush and beautiful gardens on the site.