Palau de la Música Catalana and Hospital de Sant Pau
If you have a chance to see this spot, be sure to see the inside and the outside as it is a good representation of modern Catalan art. Enjoy a concert that interests you, I went to see Buika, and the building has a different perspective if you do like sightseeing. It's worth paying to see a play and create the atmosphere for their lighting, acoustics. It is small and cozy. If you can, get tickets for the pit area on the first floor, downtown, the best views. Very nice experience.