The “great out there”. Space. The Abyss is a bottomless, surfaceless and water-filled void that surrounds Dunia. While exploration of the Abyss is only in its infancy, scientists are already convinced that the void has no end. No matter which direction you travel, you will never reach an end. It is the infinity beyond the world-dome.
People have known for centuries that the world is flat and covered by an energy dome that keeps the Abyss out. It is this construct that inspired the development of the domed megacities. The Abyss Gate technology is a result of studies involving the dome and its particular energy type.
The Abyss Gate is a huge, circular airlock coupled to a supersized subharmonic resonator. Once the airlock is sealed and the submarine vessel is suspended in place, the resonator activates and slowly phase-shifts the part of the dome that is inside the airlock's circumference. This lets abyssian water seep through the dome and fill the airlock. Once the airlock is filled, the passage into the Abyss is open and the submarine can leave. The gate is located to the east-northeast at enough distance from the periapsis of the sun to allow for safe operation.
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The Arcom Nixie is a popular personnel and cargo carrier for use in the Abyss.
HyperSonar is a data-transfer technology that uses hyper-focused rays of soundwaves to transmit data across great distances in dense mediums, like the waters of the Abyss.
Islets, also called "Death Pebbles", are small floating islands that are found in dense clusters in the Abyss. While rich in minerals and chemicals, they pose a significant navigation hazard to submarines. Particularly in areas near volcanic currents.