I think Pedro won't tell here all of his secrets about his frequented nude-beaches, because now (despite some local pervs/voyeurs) he is almost the only pro-voyeur on that beach and by that, able to shot and submit very nice pics here. But as soon as he is writing here all the nude-beach secrets, you may have an overkill of OCC pervs/voyeurs on those beaches, even those without any respect and as a result the girls will go away and he (and we here) will never get those nice shots anymore.
I can only say: go to Spain on holiday for yourself and check those beaches, may be you will see and/or met Pedro once.
But if it happens that one of you visit one of those beaches, please do not lay your towel (and sit) just a few meters away from those girls. Because that won't work, and don't forget to go nude, it's a nude beach you know!!!