Early planning: Porto to Basque

Drive Porto to Santiago de Compostela as your first stop! Why return to Porto for your outbound flight? Bilbao would work for your flight.

Seems like a lot with only 12 days. You could have a more relaxed trip if you cut out the France days. We viewed the flysch formations in Zumaia, from the beach and also from the outcrop where Érmita San Telmo is located. Check for parking before arrival since there is almost none in the upper town. We walked up to San Telmo. O’ Cebreiro can be seen in about 30 minutes. The chapel is nice as are the round houses, but it is very small. It is mainly a stop for Pilgrims walking the Camino. Parking was plentiful. We were there in the month of May and it was 32 degrees when we visited, so have some warm clothing. To me, Hondaribbia is worth a full day to see both the upper (historic) and lower towns. Burgos, León, and Santiago de Compostela are each worth full days probably two.

There are so many places and things to see that you’d need a few trips to exhaust all the options. Good luck narrowing down the trip. I’m glad you’re returning the rental to Porto to avoid the hefty one way rental fee. For ideas, photos from my 2017 northern Spain trip are on my website. We started and ended in Madrid.

I think after Porto, driving to Santiago is a great idea and then Burgos. Maybe even a stop in Astorga or Leon on your way. What about Pamplona? O Cebrio is lovely to wake up to if you can find a room. There aren't many up there, but it is a unique place to be.
Fly home from Bilbao as someone already suggested. Going all the way back to Porto is not fun.

Porto 3
Santiago de Compostela or Pontevedra 3
Vitoria Gasteiz 3
Bilbo 3
Depart from BIO

12 days seems like not a lot to combine northern Spain and Portugal, perhaps just focus on one or only combine Galicia with Northern Portugal? I'll probably get smited by the foodie gods, but I would rank cuisines as in terms of my preference:
1. Galicia
2. Asturias/Cantabria
3. Basque
4. Northern Portugal

In terms of sites, you could also add a few days in the magnificent Picos de Europa National Park. Know that April is the rainiest season in northern Spain, it's called "Green Spain" for a reason, just know you will expect a lot of rain.

And you´re missing Bilbao??

I was going to remind that one-way, cross-border car rentals can be very expensive. But do I understand correctly that you'd be driving back to return the car and fly out of Porto? That is a lot or driving, and you'd either be blowing past loads of great places to do any justice to the Basque Country, or have so many short stops that you barely see anything, anywhere.

Last month I explored western Galicia, traveling to Santiago de Compostela, A Coruña, Fisterra, Pontevedra, and Ourense. The nine days I spent felt like a reasonable minimum for the itinerary. I drove about 500kms total in the 5 days I had the car, and that was about the limit of car time I'd have wanted on a relaxed and enjoyable trip.

My thought is the same as Carlos's: I wouldn't push all the way to the Basque Country from Porto with so little time. Galicia has many points of interest; in addition to those already mentioned, I liked A Coruna and Betanzos. You'd have plenty to keep yourselves entertained if you didn't go as far as the Basque Country.

A later trip to the Basque Country would allow you enough time to see that area better. I agree that skipping Bilbao is really unfortunate, and combining Hondarribia, Bayonne and St-Jean-de-Luz in one day would be hectic. I assume a trip to the mountain villages on the French side would also be worthwhile; I didn't manage to get to that area myself, being without a car. There are always more good destinations than days available, it seems.

In terms of time required, Potes is a lovely old stone town, but I think a few hours there would be sufficient. A half a day would probably be generous if you wanted to have a leisurely meal there--unless I missed something. It really is a charming-looking little town.

The folks suggesting a return flight from Bilbao are apparently not considering the likely-very-high international drop charge for the rental car.

There is excellent bus or train service from Porto to Santiago or Vigo.
You could then pick up your car and would not have to come back to Porto and save on the one way fee. That would give your more time for your other destinations.
I also really enjoyed Picos de Europa but not sure how much snow there will still be in April.
Lots of interesting towns to pick from in Galicia, Asturias and Rioja regions.

@Suki I would love the open jaw flight option but unfortunately it was 2-300.00 cheaper to go in and out of Porto. Flight is booked. Thanks for the suggestion though!

@Jaimeelsabio Thank you for the beach parking heads up and time to spend in o Cebreiro (if we go!)
Your pictures are fantastic, I'll have to delve into them more.
It's so hard when you have such limited vacation time to narrow these things down. It's helpful to hear how long to stay in different towns when you've never been.
I considered staying in Hondarrbia but on forums people seemed to think San Sebastian had more going on. Yes all three is likely crazy talk :)

@Ms. Jo I guess my thoughts were if we do the yucky drive in one say to SS (or that area) then we'd have time to take our time driving back to Porto. Plane tkts are already paid for sometimes to get a great deal you have to deal with the stinky drive on one end :(

@davebarnes thanks for the thoughts, with departure from Bilbao out it won't work but I love the days recommended.

@carlos I'm sure the food is excellent everywhere!!! but thanks for your recommendations. I'm going to have to take all these replies into consideration.

@mikelbasquequide I'd definitely like to see Bilbao since I see you are a Basque guide so you think it is crazy to try to spend only 3 nights in the Bilbao/San Sebastian area. If not I'd love to pick your brain on what to cover.

@scudder would it be insane to just to Porto and Basque? My husband has his heart set on Basque but I agree it is a lot of driving!
Last time we were in Spain we did Barcelona flew to Malaga drove to Grenada, Sevilla, bus to Lisbon for New Years! I think it was 10 or 12 days.... we may be crazy.

@acraven yes never enough days. Thanks for all of your suggestions! Like I said this is early planning and I'm not stuck on anything except the plane in and out of Porto.... you've all given me a lot to think about thank you!