The Abyss is the title applied to the deepest part of the sea in Endless Ocean. The player can access it from the overworld through Deep Valley (which is located at coordinates F-6, G-6, and G-7), but they must have a special set of gear given to them by Katherine before they can access this area. The Abyss is a massive gash in the ocean floor, pitch-black, with four caves embedded in the walls of the canyon: Secret Cave, Crystal Cave, Fiend's Cave, and the Unnamed Cave.
During the daytime, there are hydrothermal vents at the eastern end of the Abyss spewing boiling hot water into the sea, blocking the player’s access to that area, but at night these vents shut off. This grants the player access to zoom-mode spots and treasures hidden among the vents, as well as access to the Unnamed Cave (and the coelacanths that live there).
Several notable landmarks and unique creatures can be found in the Abyss. The landmarks include the whale skeleton resting on the seafloor on the western side of the canyon, in which a large group of Sea Pigs have made their home. At night, a solitary Goblin Shark swims through the corridor formed by the dead whale’s ribs. Another skeleton, the fossilized remains of some long-dead sea creature, is found embedded in the wall to the south of the Graveyard.
Two salvageable items, in four parts each, are found scattered around the Abyss. The parts of these treasures, the Anomalocaris Fossil and Red Coral, are found mostly in the caves around the Abyss, but a couple of pieces are on the seafloor and may be inaccessible in the daytime when the hydrothermal vents are active.
Several unique or rare creatures make their home in the Abyss. These creatures include:
Oftentimes, the creatures in the Abyss respond better to the light of the Underwater Pen than they do to the normal methods of feeding or petting to unlock their information.