Lording it over the town, this formidable Renaissance structure – two churches above a crypt – sits on the site of the town's medieval parish church. It contains a rich collection of baroque art, including several paintings by José de Ribera (El Españoleto) and a fine sculpture by Juan de Mesa.
Visits are by Spanish-language guided tours, which take in a finely decorated underground mausoleum (the panteón ducal), created in 1545 as the family vault for the Dukes of Osuna.