The DisSea, a once-thriving body of water located near DisCity, is now the home to the highest concentration of spiritual contamination in the post-Nightfall world. Despite its name the DisSea is not a true sea, but rather an inland lake formed by the impact crater of the Perishing Star. In N.F. 84, the DisSea Explosion rendered the surrounding area almost entirely inhospitable, earning it the nickname of The Death Zone. Intense contamination and swarms of Apostles and other monsters constantly emerge from the DisSea, separated from DisCity only by the Broken Frontline.
As the epicenter of BR-000, the DisSea is critical to many of the greatest mysteries and conflicts in the post-Nightfall world. The Black Ring there is the largest and oldest known, and at its deepest point seems to have connected directly to the Deep Mania. This has a wide variety of effects and implications: The Phantom Moon has a strong presence in DisSea, Wandering Apostles in Whitesands and beyond are constantly moving towards DisSea, and the souls of all those who die while infected with Mania become trapped in the DisSea.
Shortly after Nightfall, the Keylan expedition sought to explore DisSea and uncover the secrets of the Perishing Star. The expedition was a disastrous loss of life, but resulted in Keylan's discovery of the Hypercube. From then on, DisCity was built on the edges of DisSea in order to mine Hypercubes from within and provide hope to the post-apocalyptic world.
Inner Bay
The Inner Bay is a region on the southwest shore of DisSea, bordering Syndicate. It was the former center of Hypercube mining before the DisSea explosion, but was completely destroyed by the calamity. Spreading contamination made the region almost completely uninhabitable, and a refuge only for those trying to avoid the gang conflicts of Syndicate. It is considered a slum even by the low standards of that district, but is also home to Drifter Camp.
Lone Island
The Lone Island is or was a location in DisSea that held great significance to the Underground. It was attacked and destroyed during the Eclipse Operation.
The Black Tower
While their consciousness was trapped in Nightmare Space, the Chief witnessed a colossal black tower emerge from the boiling water of DisSea directly beneath the Phantom Moon and at the center of the Black Ring. The Chief's approach to this tower is described as "like an infant returning to the womb." Nothing is known about this tower, but EDGE-03 implies that if the Chief were to reach the tower, it would cause a "real catastrophe" and orders their destruction if necessary to prevent it -- suggesting that such an outcome would be far worse even than the return of BR-002. The In Host's Name Crimebrand may suggest that this tower was instrumental to the origin of the Underground.