If you are staying for more than 2 nights in Barcelona, you should take the metro: it's the fastest and cheapest way of getting around, with its extensive network that connects the city with almost all the tourist attractions of Barcelona.
The metro network has 8 lines connected with "Ferrocarriles de Barcelona", serving the upper part of Barcelona and with "Renfe", the train network, that has trains to the airport and the nearby cities.
The metro in Barcelona works from Monday to Sunday.
Timetables:
Working days from Mondays to Thursdays, Sundays and public holidays: from 5.00h to 24.00h
Fridays: from 5.00h to 2.00h
Saturday: from 5.00h to 5.00h
For more information about special transport cards, click here.