Your tips Rent a bike and explore the city in a different way! Tip: rent your bike at cruising Barcelona. Nice Dutch girls and great citybikes!
Buy your ticket for the Sagrada familia in advance. You can buy them in special ATM (everywhere in the city, but not close to the Sagrada familia itself). So avoid the long queues!
Wonderful city with a good combination of culture and beach. We visit a lot of the Gaudi's master pieces. I especially loved Casa batlo and the Sagrada familia. The boat trip along the coast was a little bit disappointed.