Deep Dome is the deepest of two levels of Deep Hole. Within it, you will find, most notably, a cave blocked off by a pile of rocky rubble. When you move this rubble with the help of a dolphin partner (from a saltwater area), you will release a trapped Pygmy Sperm Whale. Along with this, a multitude of Pineconefish and a few Singular Bannerfish (under zoom-mode spots) can be found as well.
"This is the deepest part of Deep Hole. The light that reaches here has traveled a great distance from the surface and gives the place an otherworldly feeling.
It seems that another cavern may stretch out to the side, but the entrance is blocked by fallen boulders."