This fortified castle, built in the 15C for Alonso Perez de Vivero, bursar of King Juan II, served as a model for many of the fortresses belonging to the Valladolid school. The rectangular keep is flanked by four circular towers. A spiral staircase connects the different floors. In 1469, the castle played host to the Catholic Monarchs for a few days following their marriage. The building now houses the headquarters of the Cortes de Castilla y León.