Barcelona to Irun

Vibasa Bus runs an overnight bus from Barcelona Nord to Irun. Cost me around 30 euros, but I think the tickets become more expensive closer to the date of departure. You can reserve a seat online:

http://www.vibasa.es/index2.php?ididioma=2#

I thought it was great. I arrived in Irun a little before 7am, got off the bus (it drops people off at the train station) and immediately saw a yellow arrow right in front of me. Within 10 minutes I was at the albergue where the hospitalera set me up with a credencial and coffee. Very convenient.

I'm sure you can take the train, but it will almost certainly require connections.

There is a mid-day train but it arrives at 2am.
And another one at 22h00 arr 08h08 costs about €49 - more if you have a sleeping car