The Cutie Mark Crusaders go on a trip to the beach with their older sisters only to find out that it is a clothing-optional beach. They meet many of their friends at the beach and learn that there is a time and place to be nude.
Even though they are human, they are the same age as they are on the tv series and have not been aged up as equestrian girls.

There is a beach in Vancouver named Wreck Beach, and it is a Clothing Optional Beach. Other than the fact that you have to go down 500 stairs to get to the beach, everything else about this beach in the story is fiction.
Sex is only clicked because of nudity. There are no sex scenes.