Arc de Triomf Hostel in Barcelona, Spain

From Barcelona Airport (El Prat)

BUS DIRECT is the fastest: Airbus
about 5 euros worth approximately
has a frequency of 10 minutes.
http://www.aerobusbcn.com/index.php/en.html
takes you to Plaza Catalunya,
and from there you can do underground L1 (2 stops), or go on foot to the Arc de Triomphe (15 minutes).

Train, takes longer but is worth only about 1.50 euros
Trains every 30 minutes.
consultation times
http://www.renfe.com/EN/viajeros/cercanias/barcelona/index.html
But need to change at Sants station,
this transfer is very easy because when you get to Sants station,
must get off the train and wait on the same platform to a train pass now Arc de Triomf. (two stops more)

If you're in the Sants train station, it is very easy, there are many trains that pass by and make a stop at Arc de Triomf,
You can easily ask.

For more information:
http://www.barcelona-tourist-guide.com/en/airport/barcelona-airport-transport.html#AirportNightBus
Map of transport in Barcelona
http://www.tmb.cat/img/genplano.pdf

From Girona airport
Direct buses to Barcelona
North Station is right next to the hostel.
(5 minutes walk)
See schedules
http://www.barcelona-girona-airport.com/main/get/17