The Devils Hole (Hoyo el Diablo) or The Elevator:

While not an actual dive site this is a great phenomena created by a hollow in the rocks along the shoreline. When the swell is big it is more impressive. This entire hollow fills as the swell comes in and then recedes as the swell leaves. The result is a serious "hole" in the water that can easily go 1-2 stories! A boat is needed to see the Devils Hole.