I don't have any info (or experience) at hand, but am sure I saw charters advertised at Getxo Marina, Bilbao. Don't really know if there's much to explore on such a trip though, not many inlets on a very rocky coast. Although I love the area and am considering as a liveaboard base.
Jem.
Life’s a compromise – SWMBO wants to go walking in the Pyrenees and we have negotiated one week walking and one week sailing. Nearest bit of ocean that I could see!
You could always try the med end of the pyrenees - somewhere Perpignan way? Alternatively Arcachon way and drive from there to the walking bit - about 2 hours drive.