445 metres above sea level and 288 meters high, Collserola Tower in the natural park of the same name is an emblematic symbol of Barcelona since 1992 Olympic Games. The telecommunications antenna by Sir Norman Foster & Partners is located near Tibidabo Amusement Park, and I suggest you arrive early and visit both (although they are near the city it is not probable that you climb up twice). From the tenth floor of the structure you can have even higher panoramic views of Barcelona City and neighbouring towns but you need fair skies for good visibility behind the surrounding glass walls. For technical details visit the official site. Maybe you would like to see a full size image
See Collserola Tower Picture on a Google Earth Map