This monastery in the Plaza de la Encarnación square was built in the 17th century by order of Margaret of Austria, the wife of King Philip III. The building was designed by architects Juan Gómez de Mora and Fray Alberto de la Madre de Dios. The church underwent considerable refurbishments in the 18th century following a fire. The architect Ventura Rodríguez gave the church a neoclassical style, and the interior was decorated by the leading artists of the time. Some of the rooms in the monastery are open to the public today, such as the Salón de Reyes (Hall of Kings), the choir stalls, the cloister and the sacristy, where you can see works by José Ribera, Antonio Pereda, Luca Giordano, and Gregorio Fernández. However it is the Reliquary (containing a collection of 700 pieces made of bronze, coral, ivory and fine woods from Italy, Germany, Spain and the Netherlands) which is the most important and popular space in the church, and is also home to carved images by Juan de Mena and Salzillo. The relics include the phial containing the blood of Saint Pantaleon which, in a curious phenomenon, every year on 27 July returns to its liquid state.