My sister and I are going to be in Porto at the end of our Rick Steves tour of Portugal in September. We would like to fly, or take a train, or hire a driver to travel to San Sebastián when our Portugal tour ends. Does anyone have a recommendation for the best way to get to San Sebastián in Spain? My sister is not comfortable with me driving us in a rental car!
Renting a car would be costly when picking it up in one country and dropping it off in another and could incur a $1,000+ drop off fee. I don’t know of any driver since it would take over 8h to get there. Your best bet is to fly from Porto to Madrid or Barcelona to San Sebastian that will take a full day. Personally, I would reconsider seeing San Sebastian since you're wasting a day trying to get there. Assume you'll return to Europe and visit San Sebastian then.
It is kind of out of the way but there are two short direct flights Porto to Bilbao then you could get the bus to San Sebastian.
That Porto - Bilbao flight is the only viable option.
Have you considered visiting Galicia? It is not the same as the Basque Country of course, but it is at least equally lovely, and easier to get to from Porto.
Seconding Balso's comments
Flight to Bilbao
Galicia is beautiful!