Obviously, it would be a sin against modesty, and if someone was going in hopes of seeing attractive nude people, it would be deliberately courting a near occasion of sin against chastity. If you stop and think about it, going to a nude beach in hopes of seeing attractive naked people isn’t any different than watching porn on the internet. We’re not supposed to go out actively seeking temptation, there must be some kind of sin involved just in doing that, but I forget what it would be called.
You’re liable to be disappointed, however, in your quest once you get there. There used to be a nude beach on private land on Long Island. They charged admission, and the public could go there. A former coworker of mine went for no good reason. She told us that she had never seen a more varied configuration of beer bellies, varicose veins, flab, surgical scars, and body fat all exposed in all its “glory” for the world to see. Far from being an intriguing experience, she thought it was mildly nauseating. It would seem most people have an exaggerated sense of how physically attractive they are, based on her observations. The previous responder said, “you’d have to be Padre Pio to avoid sinning in that situation.” My old coworker would have said, “you’d have to have a cast iron stomach to not upchuck in that situation!”
Face it: Just about everyone looks better with clothes on.