The Pyrenees are an awesome place, particularly out of the main season, lot less domesticated than, say, the Alps. The French and Spanish sides are very different, the latter is very arid and virtually dead in the summer (to the point of struggling to find shops open), the French side is lot lusher. Both looked like some great MTBing could be had, though I am not sure what the rules about bikes are (I have a vague recollection that MTBs might not be allowed in the Parc). Also, camping is fairly limited, low down in the valleys (lot of the books and websites refer to a campsite at Bious Oumette -- this place has been demolished years back, which makes for a great surprise when you arrive past midnight
)
If you do decide to do some climbing, whatever you do, under no circumstances rely on the D. L. Walker book Rock Climbs in the Pyrenees, in my experience it describes Pyrenees from some other planet. On the other hand, if you want to set out on a mystery hunt after mythical routes and climbing locations that might have once existed, that's the guide to go for; you have been warned (though, admittedly, I am aware of no other English climbing guidebook for the area, which is a great shame.)
Some pictures from a trip couple of years back are here.