Tordesillas was a former defensive bastion against Muslim invasion. Declared to be a site of Cultural Interest in 1931, the monastery stands out because of its façade in the Almohad style, its Arabic baths and the reredos in the exceptional chapel of Saldaña. All the rooms contain elements of great architectural and decorative interest, including a clavichord which belonged to Juana la Loca.
Relevant among the ecclesiastical buildings are the church-museum of San Antolín, declared to be a site of Cultural Interest in 1998; whose main feature, a 16th-century reredos with sculptures by Juan de Juni, stands in the chapel of Alderete; and the church of Santa María, a Gothic structure which was remodelled in the 16th century in the style of El Escorial. Other points of interest in the town are the Casas del Tratado, also declared to be a site of Cultural Interest, which are two adjoining palaces that received this name because it was here the Treaty of Tordesillas was signed in 1494, by which Spain and Portugal established the division of the territories which were being colonized in the New World; the main square; a medieval bridge of 10 arches and some remains of the wall which surrounded the entire town.