Barcelona at night is also serviced by public transport, the metro runs in weekdays until 12 pm and at the weekends on Fridays until 2 am and Saturdays run all night. The bus lines that run at night are called Nit buses, they are different lines as the daytime ones and cover Barcelona city and the surrounding territory.
Something to take into account is that the Barcelona travel card and the Hola Bcn! card are not valid for the night buses since it is run by a different company.
Schedule and night bus lines
There are different bus lines at night, 17 lines to be exact, that don't follow any daytime lines, they are routes created specifically for night buses, so before relying on your knowledge, check out the bus stop or the online information in the amb website.
All the lines go through Plaça Catalunya, except N0 line, check out the map below to see from which stop does your bus line takes off. The frequency of buses is every 20 minutes, and they start running at around 10 pm, but again it depends on the line so it is best to anticipate and check it out.
Below you have the details of the stops in Plaça Catalunya and Plaça Espanya which are the main centres of the Night bus. You will find all information on the stops, destination and details of the lines in the AMB night bus website.
Take into account that since night bus lines are tailored made for the night routes, the routes take longer than normal daytime lines. This means that if you go to a near station it will work for you, but if you are going to one of the extremes of the line, it might take you more than one hour to get to your destination.
My recommendation is that if you can at all, take the metro if it is opened if you are going a bit further and you want to avoid a route of more than an hour due to the different stops in between, a taxi can be an option.
Taxis are not very expensive in Barcelona, comparing to the prices of other European cities. A general ride, of 3 to 5 km will cost you between 8 to 15 euros approximately, depending on the traffic and if there are any add ons on the rate. The capacity of the taxi is 4 people so if you fill in the taxi it will be just a few euros each, something to think about.