Well this is an Hentai (so an Hard core Manga) a really good one IMHO the synopsis is that a japanise classroom decide to run a schooltrip on south France, for the surprise of no one they finished on a nudist beach, ENF Ho!
[Shiwasu no Okina] Nudist Beach ni Shuugakuryokou de!! for the rest and even more (9 chapter long...)
internet is your friend
