Apart from the CP ticket offices, you can also buy tickets for the international trains such as the Celta, Sud Expresso and Lusitânia Comboio Hotel, at Base, Promo and Promo+ prices through the RENFE site (Spanish railway network).
CP Services: Celta (Oporto/Vigo) | Sud Expresso | Lusitânia Comboio Hotel (Lisbon/Madrid)
They can be bought for Adult, Child, Youth < 26 and Senior ≥ 60 for up to 9 people travelling together.
The tickets can be bought up to 15 minutes before the train leaves your station.
You must show the printed ticket on board the train. The tickets must be printed in colour or black and white, in portrait and normal print size l (100%), on A4 paper.
If you buy tickets for more than one person, you must print a separate ticket for each one.
These tickets can be refunded and reissued (change of class or journey date) through the RENFE site so long as the tariff allows this and up un til 15 minutes before the train starts its journey.
In the case of any difficulties in the purchase, reissue or refund process or for further details, RENFE has a help line 800 834 274.
You can also contact them by email firstname.lastname@example.org