Museo del Prado

One of the greatest art museums on earth — Velázquez's Las Meninas, Goya's Black Paintings, and the single largest collection of Bosch anywhere, including the full triptych of The Garden of Earthly Delights. Anchor of Madrid's Golden Triangle of Art along Paseo del Prado.

The collection is vast enough that trying to see everything in one visit guarantees seeing none of it properly — pick two or three wings (Velázquez, Goya, and Bosch/Flemish cover the highlights) and budget two to three hours. Free entry runs Monday to Saturday 18:00–20:00 and Sundays 17:00–19:00, though the queue for it stretches well before opening. The Prado, Reina Sofía, and Thyssen-Bornemisza all sit within a fifteen-minute walk of each other along Paseo del Prado — a combined Paseo del Arte pass covers all three at a discount.