One of the few vestiges of the 17th-century Palacio del Buen Retiro, this somewhat austere building overlooking the Parque del Buen Retiro is run as an academic library by the Museo del Prado and, as such, is mostly closed to the general public. The only exception, and it’s an important one, is for the guided visits to the stunning Hall of the Ambassadors, which is crowned by the astonishing 1697 ceiling fresco The Apotheosis of the Spanish Monarchy by Luca Giordano.

These visits can be arranged at the ‘Educación’ desk just inside the Puerta de los Jerónimos in the Museo del Prado. The remainder of the Casón del Buen Retiro has been renovated in a modern style.