The Casón del Buen Retiro is one of two buildings that survived the destruction of the Buen Retiro Palace, from which it takes its name. The former ballroom now houses the Prado Museum's study centre, where visitors can find a library specialising in art whose vault boasts painter Luca Giordano's 1697 Allegory of the Golden Fleece mural.
Built in 1637 as part of a project developed by architect Alonso Carbonell, the building's west-facing façade was designed by Ricardo Velázquez Bosco. The latest restoration work was undertaken by Jaime Tarruel and completed in 2007.
For decades, it was home to 19th-century painting collections belonging to the Prado Museum, with around 3,000 pieces in total. It even exhibited Picasso's Guernica when the masterpiece first arrived back from the US, but, in 1992, it was moved to the Reina Sofía Museum after the Casón del Buen Retiro was closed to undergo major renovation work.
Today, the newly-restored building houses the Prado Museum's library—one of the best and lesser-known art libraries in Spain—which specialises in paintings and sculptures from the Middle Ages up until the 19th century. Visitors can also find a large collection of drawings, stamps, classic sculptures and decorative art pieces. In addition to its more than 100,000 books (including monographs and reference works), 1,500 periodicals, 260 auction catalogues, audiovisual material, specialised digital resources, posters and brochures, the centre also preserves an impressive bibliographic heritage of prints and manuscripts produced prior to 1910. These are of extreme significance because of their considerable quantity (7,000 volumes), their specific subject matter (painting, architecture, festive booklets, sketch pads and books on iconography, emblems, works on anatomy and physiognomy, etc.), and the scarcity of some of the publications.