The Paseo del Prado is the densest mile of art in Europe and one of the easiest walks in Madrid — a straight, shaded promenade with a major gallery roughly every two hundred metres. Come in the morning, before the queues set.
Under three kilometres, and the only hills are the museum staircases. Begin at the Fuente de Cibeles, the chariot fountain at the top, and walk south. The Thyssen-Bornemisza comes first — the private collection that quietly fills every gap the others leave. Past the Fuente de Neptuno stands the Prado itself, holding Las Meninas and Goya's darkest rooms; pick three galleries and don't apologise for skipping the rest.
The surprise is at the bottom. CaixaForum hangs a rusted-iron box above a sunken plaza, and beside it a whole wall has been planted green — Patrick Blanc's jardín vertical (vertical garden), four storeys of living plants on a blind gable.
End at the railings of the Real Jardín Botánico, with Atocha and the Metro a short drop below.