Museo Reina Sofia

Set in a massive 18th-century hospital building dramatically expanded by architect Jean Nouvel a decade ago, Spain’s official modern and contemporary art museum can seem like a daylong undertaking. But visitors should feel comfortable dipping into the galleries that appeal to them and breezing past others. Just don't overlook the works by 20th-century masters Salvador Dalí, Juan Gris, Joan Miró, and of course Pablo Picasso, whose mural-sized Guernica, depicting the horrors of aerial bombing in the Spanish Civil War, ranks among the most iconic—and moving—images of the 20th century.