We often get suggestions (in response to vague requests for help) throwing up well intentioned ideas on places bods can go to / through / stay in, only to then learn:
A. That they only have a week’s holiday, of which two days will be lost getting to and from their home, before they even set foot on foreign soil. This is a common phenomenon on these pages.
B. That, only later, they have “Done Spain, mate” and really fancy going to Germany.
With a bit of gentle prompting and a touch of filling out of the OP’s (deliberately vague) opening post we now know:
A. That the OP has “About a week / 10 days” for (we can only assume) his entire door-to-door holiday which might (or might not) dictate or limit the sea crossings and / or control how he gets from Santander back to Aberdeen ie. well north o’ the border.
B, That he’s “Done northern Spain” but, even so, doesn’t mind doing it again. But, he did mention returning via France and / or Ireland.
Now all we wait to hear is whether the week / 10 days really is door-to-door or if it isn’t, what the door-to-door period is. The combined whit and wit of UKGSer can then be channelled into providing the fellow with as many combinations of return routes as there are quills on a porcupine.
PS A reminder that the OP wants:
…. a gentle saunter back to Aberdeen….
from Santander. I guess 400 mile days every day are not on the cards.