I rode Sustrans route 47 from Swansea to Pontypridd in a day- there’s a few photos here:
http://www.flickr.com/photos/manicstreetpreacher/sets/72157624036776395/
It was my first time bike touring- I went on to Cardiff, then did the Taff Trail up to Brecon, Abergavenny, Hay-on-Wye, down to Bristol/Bath and then home to Oxford :)
PS. Make sure you get a bike reservation, some companies refuse to take bikes without one at peak times.