In reply to Sam Mayfield:
We stayed on the coast in Ribadesella for a couple of weeks a couple of years ago. Nice seaside resort with mainly spanish tourists, some surfers (main reason I was there, basically), and folk passing through on the Camino de Santiago etc pilgrimage. Really nice place. Llanes is too, but a little quieter.
Anyway, the foothills of the Picos run right down to the sea, and have some pretty good off-road bike riding (I was getting miles in for the 3 peaks cyclocross). Bit of an underrated area and really really quiet (end of Aug, first week Sept). I also did a horrendously scary ride along the Cares gorge, on a terrace below the main tourist route. Not difficult but failure = death. Anyway...
You can't really drive across the main Picos, so need to decide which side you want to access. From Ribadesella it's a 20 min drive to Cangas de Onis, gateway small town to that side of the range. Also a nice place and v outdoor stuff orientated. Did a few good walks to and around refugios etc. What's marked as a track on the map can turn out to be a fair scramble. Anyway, brilliant area and would love to go back on a proper mountain orientated trip. (Though may struggle if the surf was good.)