You are in Barcelona but at the same time you feel you can watch the skyline from the distance and abstract yourself from the context. Certainly Maremagnum is a must see. The Aquarium, the paintings market under the front pergola and the 3D IMAX movie theater are recommended visits.
As previous posts just offered details I thought it would be better to show the whole scene as seen from Montjuic mountain. Don't forget La Barceloneta in the background