<map lat='43.311939092640564' lng='-1.9820022583007812' zoom='13' view='0' float='right'/> Donostia (Spanish: San Sebastian) is a city in the Basque Country, in the north of Spain near the French border.
1) Try the petrol station closest to the city centre at Av de Navarra/Calle de Zemoriya. Hitchhikers have found French cars here.
2) Take the local train to Irun and walk to the motorway. At the border there is a toll-gate, where you can ask for lifts. It's easy to go to Bordeaux.
From the Irun motorway toll-gate, it should also be possible to find a ride heading into Spain or to Portugal.