Water Gym

What better place for there to be a water gym? You have sun, sand, water, and a continuous stream of people; all making for a great water type gym. Sitting out in the ocean, the gym is only able to be accessed from a large underwater opening, whether you swim by yourself to it, or use your water pokemon to get you there. Once you get inside, you notice that the opening was not only an entrance, but also the battle field.