Barcelona's airport is 12km southwest of the city at El Prat de Llobregat, was built when the city was a much less popular destination, and is now expanding to cope with the strain. The airport is linked to the city by regular and direct train or bus services. The train (6am-10.40pm; journey time 30min; 2 weekdays, 2.30 weekends and public holidays; info on 934 811 299) runs every thirty minutes to Sants Estació and - more usefully if you're staying in the Barri Gòtic - continues to the station at Plaça de Catalunya and on to Arc de Triomf, with the exception of the very last train which terminates in Sants. Buy your ticket from the automatic vending machine at the platform (you don't need the exact change) or at the ticket office. There's also a very useful Aerobús service (Mon-Fri 5.30am-11pm, Sat & Sun 6am-11.30pm; 3) which leaves every fifteen minutes from outside both terminals, stopping in the city at Plaça d'Espanya, Gran Via (at c/Comte d'Urgell), Plaça Universitat, Plaça de Catalunya (in front of El Corte Inglés) and Passeig de Gràcia (at c/la Diputació) - this takes around thirty minutes to reach Plaça de Catalunya, though allow longer in the rush hour.
There is a second bus connection from the airport that's not as convenient but does run throughout the night at irregular intervals: bus #EN, leaving at 10.15pm, 11.25pm, 12.30am, 1.35am and 2.40am for Plaça d'Espanya (just south of Sants Estació).
A taxi from the airport costs roughly 20.50 to Sants Estació, and 21-22.50 to somewhere more central in the old town. There's a list of current prices posted inside the airport near the baggage reclamation area.
There's an information office in each terminal of the airport, as well as exchange facilities and car rental offices