The pantheon of the Dukes of Osuna was built in the Plateresque style in 1545, as is the delightful patio preceding it. The chapel, just below the Colegiata's main altar, has three naves and a coro with polychrome coffered vaults, now blackened by candle smoke. In the crypt are the tombs of the most important dukes of Osuna and the founders of the collegiate church.