Barcelona grew in one of the world most important and visited tourist cities in the world, with flights arriving non-stop from many international airports day and night.
Here you can find all the options you have to get to the city center of Barcelona from the El Prat Airport (BCN), by train, bus, taxi.
Cheapest way to get to the city center and very convenient by day and night is to use the public transportation system. The fastes way from Terminal 2 is to go by RENFE Train, is abouth 30min to Passeig de Gracia. From Terminal 1 you can only go directly by bus or by metro, but i recommend you to go by bus as is faster than the metro. During the night from 12PM to 5:30AM your only option is to take the N17 Bus that goes all night long to the city center of Barcelona.