In reply to seanbastard:
Have you been to Albarracin before?
I was thinking about doing a public transport trip there earlier this year and decided to go to Siurana instead because the walk from the campsite in Albarracin to the boulders is probably 1 to 1.5 hours uphill everyday.
Whilst not too bad I imagine it would get very tedious doing that walk every day with a big pad.
As to the trains. We used the RENFE trains with very big kit bags and that was fine. I wouldn't expect major problems with a pad but they do have baggage guidelines so could potentially make a fuss...
Have a great trip!
Gwilym