A very Useful book to get hold of is Toby Ballentine's 'Motorcycle Journeys through Western Europe' ( Whitehorse press via Amazon).
It's full of useful easy to read information and there is a very good section on Northern Spain and the Picos, with recommended rides , places to eat and stay.
I used it as a base for planning a trip in the Western Pyrenees a few months ago, and found some of his suggestions excellent.