I do not know your age, but if you are +60, you can get a 25% discount on all train travel in Spein for 12 months, for only 6 €. Train travel in Spain is cheap, anyway, and a great way to travel.
Discount with Renfe Tarjeta Dorada for seniors and retirees âś… Up to 40% off on AVE (high-speed), Alvia, Avant (mid-distance high speed), Larga Distancia and Media Distancia (long and mid-distance) trains.
www.renfe.com
Going to Pamplona, Madrid or Barcelona are your best bets. From Barcelona there are +20 train departures to Pamplona per day from the Sants station. It is a really nice some 5h ride where you can enjoy the Spanish landscapes, have a toast/vino in the restaurant wagon, arrive in Pamploan early afternoon/evening, take a taxi/bus to Roncesvalles, and start walking the next day.
Alternatively, take the night in Barcelona/Pamplona and get rid of the jet lag, and continue next morning.