If you are planning to travel by car... I guess the first idea would be getting the N-I straight into Bilbao, and then travel along the A8 to Santander. But then you would be going up and down the same motorway on your way back to Zaragoza, so... I would recommend (specially if you are in a hurry) to follow the N-I until Burgos. Stop in Burgos, and enjoy the fact that finally the scaffolding at the cathedral is gone, and don´t forget to eat morcilla (black pudding, but it is yummy). From Burgos (excuse me, but I don´t remember the road numbers right now), I would drive along the road to Santander, I think it is the N642 ( http://www.dgt.es , it is useful, but I am afraid it is only in Spanish...), that calls up to Torrelavega. Then, after your stay in Cantabria, you could head into the Basque Country, and then to Zaragoza and Barcelona.

This is a first rough sketch, but I think that with the help of a few URLs as the ones below, you will be able to come up with a nice itinerary. Time of the year is very important, remember, August can be crazy

http://turismo.cantabria.org/ http://www.spaintour.com/verde.htm http://www.tourspain.es/ http://bilbaoweb.com/ http://www.tuciudad.com/index.htm (check the Webcams)

Good luck with your planning.

Rgds from Covadonga in Bilbao (Spain)