We rode on the tourist buses that venture all over Barcelona. We didn't get to start the tour until Tara got off work so we didn't take full advantage of all that the tour buses offer - but it was neat to see the city and give our feet a rest. The buses make frequent stops and allow you to get on and off at any stop and visit any sight for the amount of time you wish- you just hop on the next bus that comes by.
We rode the red line and visited Park Guell which is a park designed by Gaudi. It was apparently originally supposed to be a housing subdivision but only two houses were built. The park is gorgeous and has the dragon fountain that is on so many post cards!
We saw two brides and grooms while walking around the park and it was obvious why they wanted their wedding photos taken at the park - the setting was beautiful and there were views out over the city and you could see all the way to the sea.