I noticed after our Rick Steves trip to Greece a lot of people extended their vacations on the island of Naxos. I'm wondering if there is a logical place to go to relax after The Best of Spain trip.
BoS ends in Sevilla. How do you envision the trip extension? Do you want to stick to public transport? How many days do you have to work with?
You can take a direct bus from Seville to Tavira, PT (2h).
After our Best of Spain trip, we trained to Cordoba and stayed 2 nights there. The Mesquite is worth seeing. then trained on to Madrid where we flew out of.
There is no "logical" place to go to relax. What are you interested in doing to "relax"? A beach?
Depends on when your trip is, but for a beach area to relax after Sevilla kinda like a Greek Island you can try Costa de la Luz, due just south-east. Beach towns like Conil de la Frontera or Zahara de los Atunes would be around where you would look.
Further afield you have the Algarve region in southern Portugal, I believe there is bus service from Sevilla to the regional capital of Faro.
The length of the trip extension might elicit better responses as would things you like to do.
To me, sitting on a beach isn’t relaxing while looking at old buildings and walking around small towns is.
Maybe Arcos de la Frontera?
I am done. The end.