The Casón del Buen Retiro is one of the two buildings that survived the destruction of the Buen Retiro Palace, from which its name was taken. Currently, it is part of the Prado Museum.

It was built in 1637 as part of a project developed by Alonso Carbonell. It still maintains the windowed barrel vault and the Alegoría del Toisón de Oro fresco painting, done by Lucas Jordán in 1962. The main west façade was designed by Velázquez Bosco. Jaime Torruell performed the latest restoration.

For many decades, the building housed 19th Century painting collections belonging to the Prado Museum, comprising about 3,000 paintings. Moreover, it exhibited Picasso’s “Guernica” since the arrival of the painting from the United States of America. In 1992, Picasso’s work was moved to the Reina Sofía Museum, and the Casón was closed and underwent a major restoration.

Today, newly-restored it houses the library of the Prado Museum, one of the best and most unknown libraries of art in Madrid. It is specialized in painting and sculpture from the Middle Ages until the 19th century. It houses a collection of more than 150,000 books, including monographs and reference works, 1,500 periodicals, 260 auction catalogues, audiovisual material, specialised digital resources, posters and leaflets and it preserves an outstanding bibliographic heritage, of prints and manuscripts prior to 1900, of significance due to their number (7,000 volumes), their specialised nature (treatises on painting and architecture, festivity programmes, drawing charts and iconography books, emblems, anatomy and physiognomy) and the rarity of some of the copies.