Museo del Prado

The main Spanish national museum, founded in 1819, houses European art from the 12th to early 20th centuries, anchored by the former Spanish royal collection.

Look for the pockmarks on the exterior? No — that's another landmark. Instead, inside, find the 'Black Paintings' by Goya, among the most intense works in the collection. Tip: head to Room 67 for Velázquez's 'Las Meninas' early, before the crowds.