Starting at Sea Level Pamplona is at 1,500ft. I suggest 4,500ft min as the Basque Counrty is very crinkly and doesn't lend itself to too much low level valley stuff, and I was a bit pissed when adding the waypoints and mistook the ridge top border with a road, so much lower and you hit a ridge ( hand fly? my fav) if using GPS.
The entire flight is outside of the 'Spanish' Basque Country but culturally the entire route is generally considered by Basque people to be Basque.
And a really Beautiful place to visit with little towns and villages steeped in individuality and flavour scattered amoungs the various hills and valleys that make up the Basque Country, and a couple of very vibrant Cities.