It forms a large square enclosure closed by a semi-circular apse and covered by a Casetonada dome, with Lantern.
Two small chapels with their sacristies are opened on the sides; On these areas are located grandstands that open to the main space. They contribute to the lighting of the enclosure two stained glass windows made in 1574 by Vicente Menardo, who have undergone numerous subsequent restorations. The work of this chapel was designed and directed by the architect Martín de Gainza from 1541. In 1556, with the death of this architect, the work was complete except for the cupola, which had to conclude towards 1568 the architect Hernán Ruiz II; The exterior of this dome is compartmentalized with caissons in which the heads of Kings were included. The Dome lantern sank in 1754, being rebuilt by Sebastian van der Borch. The tombs located in the open niches in the lateral walls keep the remains of Alfonso X the wise and his mother Beatriz de DeSavia. The chapel is chaired by an altarpiece made towards 1646 by Luis Ortiz de Vargas, where, in the main niche and under a silver canopy is worshipped the image of the Virgin of the Kings, this being a gothic figure of the 13th century of French origin. At his feet, embraced by the staircase is the Silver sepulchre of San Fernando and under the crypt that houses the remains of Don Pedro, the righteous king.