I recommend the bus from Santiago which stops at the airport on the way to Porto. We were warned not to take the train by friends who had done so and regretted it. I booked seats with Alsa on line but could not pay using any of our credit or debit cards. We live in England. However they do accept payment by Paypal. I am warning you of this because I had to phone Spain to find out why my cards "failed". The bus takes you to, or near, places you will have walked through on the caminho. "Bom caminho!) to you. Maricristina