Palau de la Música Catalana

This art nouveau gem designed by Lluís Domènech i Montaner has been Barcelona’s preeminent music hall since its founding in 1908. Colorful ceramics, ornate sculptures, and busts of illustrious composers—Wagner, Beethoven, Bach—decorate the redbrick exterior, but that only hints at what you’ll find inside. Among the flamboyant details: walls and columns clad from floor to ceiling in floral-themed mosaic tiles, magnificent stained-glass windows, and, centered above the 2,000-seat main auditorium, an enormous, multicolored skylight that resembles an inverted dome. Seeing a classical concert here is a treat—the acoustics are superb—but you can also sign up for a 55-minute guided tour of this UNESCO World Heritage Site; the cost is 18 euros (about $20).