The Art Museum Prado houses much of the art of Diego Velàzquez and Bartolomé Esteban Murillo. Before we visited the Prado, we had never even heard of them. Ever since we are extremely fond of Spanish 17th Century art, and every time we go to an art museum we look for them.
We also saw other must-see sights like Puerta del Sol, Plaza Mayor, the exteriors of the Castle, the Retiro Park, and further away El Escorial and Toledo. Madrid was very pleasurable and the climate was lovely.