There are many organize tours that you can do in Barcelona, the city bus tour alone could get you anywhere significant for a one day ticket. During daytime the great catch would most probably be Barcelona Montserrat. The Benedictine Monk retreat at Montserrat presents you some of the most spectacular overviews of Catalunya from the mountaintop. You will also learn about the holy grotto, the famous Montserrat Choir boys, whose music is very popular throughout the world. It is also a good idea to schedule at least one day in your visit to take mountain walks.

But if you would rather like to tour the city at night, some sights most appropriate are the musical fountains in Placa d' Espanya; the Casa Batllo which is not only unique but such a magnificent building; the Torre Agbar, a skyscraper beauty. And of course the city views from Montjuic hill. If you are simply a fun-lover and you like parties, music and limelight's, Olympic Port is just the place to be. It has a large number of restaurants, bars and other establishments which have made Barcelona's nightlife even more intense. You could also check in to some Barcelona hotels near the area if you think it's rather the place you want to stay close to.
Another ?must go? is La Rambla. It's the most famous boulevard in Barcelona. You should catch the street performers that cheer vitally to tourists. And just a few blocks south of its north end you'll find La Boqueria, a very large market where you can buy most of the local foods and delicacies. There's also the L'Aquarium, which is the second largest aquarium in Europe. You can discover a huge variety of fishes, penguins and sharks in this interactive sea-life museum.
If you happen to admire churches that still exist from history with works of architecture that is both fascinating and interesting then check out the cathedrals of Santa Eulalia and the Gothic Church of Santa Maria del Pi. Also worth the visit is the Gothic Basilica of Santa Maria del Mar, near the Picasso Museum. The Sant Pau del Camp is a romanesque church that's one of a few in Barcelona, a befitting place to go for quietude. And the La Placa Reial is located next to La Rambla in the Ciutat Vella and is considered to be one of the most beautiful squares in the world and get to see the beautiful Gaudi streetlights.
Barcelona is a charming city. Anyone who had been here could only say the most beautiful things to share for the world.