In reply to Lenin:
Deciding where you want to go might help, or at least when. The southern mountains will almost certainly be too hot for walking in Summer, so Picos de Europa/Pyrenees would be better (although these were still warm when we were camping in September). Rodellar has a lot of canyoning and swimming as well as climbing, so you can avoid the heat, but again, we were camping, so can't recommend anywhere specific.