It would be remiss to not take a day or two to go the tourist route - it's popular for a reason, you know. It means modernism; it means Gaudi; it means going up the hill to Parc Guell, and to gawk at Sagrada Familia, and to walk zig-zag through Eixample to see the most stunning modernisme architecture. It also means going down Las Ramblas, if nothing else, just so you won't have to again.
Or you could just spend a week on the beach. There's always something on, whether it's for the culture, the party or just relaxation that Barcelona beckoned.