Cant get much better than Potes. You're right on the edge of the Picos there, so about 60 miles south west of Santander. Haved stayed at this place
http://www.campingencantabria.com/el-camping" onclick="window.open(this.href);return false; three times and in the citadel town of Potes itself, just a ten minute walk away, in a hotel called La Familia. Nice and clean and serves delicious tapas at the bar. However this was in 2007 and its a rapidly changinge world we live in so google it first just in case the place is now a cash converter store.
Otherwise when you leave Santander go west along the coast as best as possible to Vincente de la Barquera for another great campsite. Cant remember its name though. But staying a close to the coast wherever possible brings up loads of pretty campsites so that my recommendation to you.
Remember to visit the caves at Altamira? Brilliant for kids and adults alike. Wikipedia reads
http://en.wikipedia.org/wiki/Altamira_(cave" onclick="window.open(this.href);return false;)
Hasta luego!
Stuart