For 2 centuries this was the nerve center of Brazil, serving as vice-regal palace and then as the seat of imperial power from 1808 until the fall of the monarchy in 1888. It's a pleasingly simple structure, long, low, and rectangular, its many high-ceilinged rooms arranged around a pair of cool interior courtyards. Nowadays it serves as an exhibition hall for traveling cultural exhibits. A room on the ground floor charts the history of the palace, with maps, paintings, and engravings. Allow about an hour. The Café do Paço cafe in the ground-floor courtyard is a great place to take refuge on hot afternoons in Rio (open the same hours as the museum).