Basilica of the Sagrada Familia
As well as being one of the most astonishing churches in the world, La Sagrada Familia is a true symbol of Barcelona. The masterpiece of the modernist genius Antoni Gaudí, this church—begun in 1882 and not yet completed—is his most widely beloved worked of art. The main chapel is unbelievably beautiful; sometimes masses are held here. To avoid the queues, book your tickets in advance online.