Madrid's great sights cluster along and around the Paseo del Prado. The three world-class museums — Prado, Reina Sofía, and Thyssen-Bornemisza — form the "Golden Triangle of Art" and between them hold one of the densest concentrations of important European painting anywhere. Allow a full morning for the Prado alone.
Between museum visits, the Royal Palace is the largest functioning royal residence in Europe, and the nearby Plaza Mayor (1619) is the great square of Habsburg Madrid. Retiro Park — once royal hunting grounds — offers a Victorian greenhouse, the Crystal Palace on a lake, and Sunday afternoons full of Madrileños. For something quieter, the Botanical Garden next to the Prado is a beautiful escape from the city streets; the small Temple of Debod — an Egyptian temple gifted to Spain — sits on a hill with one of the best sunset views in Madrid.
Madrid is also a city of great smaller museums. The Museo Sorolla, in the painter's own house, is an under-visited gem, and the CaixaForum with its vertical garden is an architectural as well as cultural stop.