Barcelona is an awe-inspiring destination, thanks in great part to the Spanish architect Antoni Gaudí. When you’re done marveling at the still-unfinished Sagrada Família, head to the center of the city to see another one of Gaudí’s masterpieces. Casa Batlló is a house that was redesigned by the architect in 1904, notable for its irregular windows, lack of straight lines, mosaic-decorated façade, arched roof, and overall skeleton-like structure.