Barcelona's hyperactive tourist office offers plenty of information and maps, and can book last minute hotel reservations as well.
They run a number of popular guided tours in English.
They sell tickets for concerts, events, Barcelona and Espanyol football matches and other sporting events, museums, Flamenco shows and attractions, and often offer discounts on GoCars, Cooltra Scooters, etc) if you use their website to book online in advance.
They also offer a vast array of walking (and running and bicycle and bus and sailing) tours, often in English one or two days a week. Special interests range from Gaudí, Picasso, the Barri Gòtic (by day or night), the Marina, Modernisme, Movies, the Civil War, Shopping, Tapas, the Park Güell, Collserola scenery and birds to Bohemian, Literary, Gourmet or New Barcelona (Poble Nou). Recent additions include segway tours, and a beach bike tour of the city's waterfront.
Check their website for schedules and bookings—there's nearly always a discount if you purchase your tour on line. Prices range widely, depending on the tour.
Find them at:
17 Plaça de Catalunya (down the steps): the main office and headquarters, open daily 8.30am-8.30pm
In the Ajuntament, Plaça Sant Jaume: open Mon-Fri 8.30am-8pm, Sat 9am-7pm; Sun and hols 9am-2pm.
Estació de Sants, Plaça dels Països Catalans, open daily 8am-8pm.
Airport Terminals 1 & 2: daily 8am-8.30pm.
Rambla dels Estudis : daily 8.30am-8.30pm
Columbus Monument: daily 9.30am-3.30pm
Plaça d'Espanya: July-Sept 8.30am-7.30pm; Oct-June 9am-3pm
Sagrada Família July-Sept 8.30am-7.30pm; Oct-June 9am-3pm
Estació Nord (bus station): 9am-3pm
Image by Terrazzo