Go to Parq Guell (another Gaudi gem in Barcelona) and take a trip to Montserrat.  Montserrat is about an hour away, but it's a nice train ride followed by either another train or a tram up to the monastery on top of the mountain.  Go early and get tickets to see the boys choir perform.  It's really a nice half-day trip.

Also, there are hundreds of places to get tapas in Barcelona (and Madrid for that matter).  My favorite throughout all of Spain is in Barcelona--- La Flauta Aribau and eat (right by the Universitat metro stop).  The tapas are extraordinary, the prices are low and the service is top notch.  Get the octopus, which is incredible.