Museo Cerralbo

A 19th-century aristocrat's mansion frozen exactly as he left it in 1922 — a ballroom lined in gold leaf, armour, tapestries, and a small El Greco tucked among furniture he actually used. Madrid's answer to a life-sized dollhouse of the Belle Époque.

The mirrored ballroom on the ground floor is the highlight — designed to make the modestly sized room feel palatial, and it still works. Free entry applies Thursday evenings and all day Sunday. It's a five-minute walk from Plaza de España, easy to combine with Templo de Debod on the same afternoon.