There are numerous tourist information offices located in the city center of Barcelona that provide the updated information about attractions, museums, events, festivals, and sightseeing.  Look for big signs with letter "i". They are run by Barcelona City Council (Ajuntament) and Catalan government (Generalitat).

Both have helpful and detailed web sites:

These tourist offices are very useful for visitors as they sell transportation tickets, tourist maps, and travel guides. You also can buy Barcelona Card here, which has special offers and discounts on public transport and entertainment venues, also can be used for special deals at  museums, night clubs, shops, and restaurants.

The main Barcelona tourist office, which covers a surface area of 700 m2 is located in (or, to be exact, under) Placa Catalunya Square. The easiest way to locate it is to first find a massive shopping mall El Cortes Ingles, and then look for large columns which pinpoint the entrances to the tourist office. They carry the information sign - letter "i" on the top. This tourist center has a handy money exchange kiosk and Internet access, and also a gift shop with a nice collection of souvenirs.

Centre D'informació Turisme De Barcelona
Pl. Catalunya, 17 (Eixample)
Open daily: 9am. to 9pm

Other tourist offices are strategically located around the city including at the airport and at the railway station.

 

More info here!