2024 Sep/Oct Lisbon, Andalusia, Basque, Barcelona itinerary

Fly to Seville and immediately rent a car and drive to Cordoba for 2 nights,
Drive only to Granada for 2 nights,
Drive back to Seville, check in the car, stay 3 nights

You don’t need a car to travel to all of theses destinations. You can easily travel by train from Sevilla to Córdoba, then via train, or ALSA bus to/from Granada and to Sevilla.
The Alsa bus has more time options than the train. The Alsa buses are comfortable and air conditioned.

In terms of weather, October will still be warm/ hot in Andalucía.

I’ve not visited the Basque Region so will let others chime in.

Edited to add.
On your previous post you mentioned that you like to take your time visiting each destination.
Given your itinerary for Andalucía, it looks like the opposite of what you prefer.
Keep in mind that 2 nights translates to one full day, and 3 nights translates to 2 full days to experience each of your destinations. Consider adding at least one more night to Córdoba & Granada, and a couple of nights to Sevilla.
My 2 cents 😉

Wishing you a wonderful trip!

Six days in Donostia-San Sebastian may be too much, there´s not that much to do there, and you´re skipping Bilbao, a city with a beautiful old quarter, great architecture, practically the same gastronomic atmosphere than D-SS and of course a must-see, the Guggenheim museum, even if just from the outside. And many great visits in the area around Bilbao. Take into account that the Basque Country may be quite rainy, so six days in the rainiest city in Spain (Donostia-San Sebastian) may not always guarantee good weather. Not much to see in Pamplona, either, it´s an hour drive so you can visit this small city in one morning, really.

I agree with the points made by the others and will add:

Northern Spain will be much cooler than the south and likely wetter. The earlier in the trip you can get up there, the better.

As you are aware, ground transportation between Spain and Portugal is limited. I wouldn't want to take two flights back and forth. Look at multi-city airline tickets into Spain and back from Portugal or vice versa. My preference would be an itinerary like this: Lisbon - fly to Bilbao - train (or fly if you must) to Barcelona - train to Madrid-Cordoba-Seville-Granada (last three in any order). I'm doubtful about convenient flights home beginning in Granada, so you might well have to head to Malaga (nice city) or back to Madrid for your return flight. Alternatively, you could fly from Barcelona to Granada and then travel to Seville-Cordoba-Madrid by train. That would position you well for the flight home.

There's one early train from Donostia-San Sebastian to Barcelona that takes only 6 hours. Although flying would presumably be a bit faster, I'd choose the train. It might be quite a scenic ride, and I hate mid-trip flights.

I liked Hondarribia (very close to San Sebastian) more than Pamplona. You can get there, and to Bayonne, by public transportation.

There's good bus service between Bilbao and San Sebastian. The train is very scenic but extraordinarily slow. Pesa has hourly buses from the Bilbao Airport to SS, departing at 45 minutes after the hour. Travel time is about 80 minutes.

Priscilla, thanks for reminding me of our own desire to slow down! And I love hearing that Cordoba, Seville, and Granada are accessible without a rental car! We’ve found that even when a target site can be done by a day trip, even a couple nights gives us a deeper feeling for a city.

MickelBasqueGuide, thanks for your insights! I’ll need to research Bilbao for a couple of overnights and fewer in San Sebastián. We hate to checkin and checkout every 3 nights, but we enjoy staying in a location overnight as opposed to trying to see it on a day trip, even when the two locations are only an hour or two from each other. We will have to analyze those trade offs. Based on Sep/Oct weather, we’re thinking that the Basque area should come first with southern Spain later, would you agree?

Acraven, thanks for your continuing input, it certainly makes sense to visit the Basque area first for the best weather. And I’m happy to hear that trains and busses can be utilized instead of renting, driving, and parking a car! I was thinking and hoping that our U.S.A. inbound flight (through AMS or Paris or London) could carry us to Lisbon, so we’d only have one flight from Portugal to Spain. Probably return to USA from Barcelona. Seems like every stop should be 3 nights, but we’d like a couple spots for 4-5 nights to rest, laundry, relax. To include all our stops probably requires more like 4 weeks instead of three weeks. What multiple-night city would you drop off: Bilbao, San Sebastian/Bayonne, Barcelona, Seville, Cordoba, Granada, (Malaga or other coastal city), and maybe Lisbon for last?
Our first stop probably deserves 4 nights because of the recovery/time adjust from USA flight?
In the same city order the nights could be: 4, 3, 5, 3, 3, 3, 3, 5. That’s an extra night in Lisbon to get up and go to the airport early. Adds up to 29 nights which is maybe 7 too many for us?
Flying both into and out of Portugal might be Bilbao, San Sebastian/Bayonne, LISBON, Seville, Cordoba, Granada, Malaga, and Barcelona for last? 4,3,5,3,3,3,3,5 which is still 29.
If I cut a day each from Cordoba, Granada, Malaga that’s 26… maybe doable?

You absolutely do NOT need a car to drive from Seville to Cordoba to Granada. A car would be so stressful. The trains and buses in Spain are wonderful. That is what we used to go from Madrid, to Toledo, to Cordoba, to Granada, to Malaga, and then to Seville.. We used ALSA bus for several trips. The buses are clean, air-conditioned, and very comfortable. Regarding trains versus buses, you should make your decision based on their schedules and what works best for you.

If you want to cut back on days, you can definitely see a lot if you spend 2 nights each in Cordoba, Granada, and Malaga. That is what we did. While it would have been nice to have an extra night in each of these places, it is not necessary.

For guidebooks, I also recommend Lonely Planet, Rough Guides, Fodors, and Michelin Green Guides. I would never rely only on Rick Steves because he omits really nice destinations from his books. For example, he treats Malaga like it's nothing more than a transportation hub, and that is not true at all. Malaga is a lovely small city with many, many interesting sites.

If I'm understanding your proposed day allocation correctly, the one that concerns me is Seville at 3 nights. Seville's not small, and it has a lot of sights. However, I don't see a place from which you can grab a night if you are already thinking of cutting Cordoba, Granada and Malaga to 2 nights.

I suppose you could drop Malaga, figuring you may well want to go back to southern Spain for some extra time in cities you see this year and could then include Malaga, Jerez, Ronda, the white villages and Ubeda/Baeza. Yes, there's always more to see in Spain.