Even on a tight schedule, Museo del Prado earns the hours.
Allow 2.5–4 hours.
One of the three or four greatest painting collections on earth, and Las Meninas alone justifies the trip. The catch is scale and density — it's overwhelming in one go, and the free evening window (Mon–Sat 18:00–20:00) packs the rooms shoulder-to-shoulder, so first thing in the morning is the calm play.