The “great out there”. Space. The Abyss is a bottomless, surfaceless and water-filled void that surrounds the world of Dunia. The void has no end, no matter which direction you travel, or how far, you will never reach an end. It is the infinity beyond the world-dome.

The people of Dunia found out relatively early in history that the world was flat and covered by an energy dome. The world just ends at the dome and the dome is impenetrable. Outside the dome looms an impenetrable darkness. At the time of this discovery they knew nothing of the Abyss. Just that there was "something" out there.


The Abyss does not have gravity, unless you're near a floating island, and once the Dunians figured out how to pass the dome and start exploring the Abyss, the submarines that were built for exploration were built taking this in mind. The Abyss is mostly empty water with occasional floating landmasses, referred to as islets. While visually and texturally similar to water, the abyssian waters exhibit different properties than that of Dunian water.

Abyssian Water

One does not go swimming in the Abyss and live to tell the tale. While the Abyss, peculiarly, have little water pressure (equivalent to about 15-20 meters depth on Earth throughout, with slightly higher pressure near large islands), it is freezing. Depending on location, temperatures range from -5 to -60 degrees Celsius, yet the abyssian water doesn’t freeze solid unless it comes into contact with air and settles. Horror stories of colonies that have experienced a breach tell of people freezing to death in icy water that solidifies as soon as it comes to rest, turning the base into an eerie tomb enclosed in ice. The same happens with ruptured or crashed submarines. The air cause the abyssian water to freeze once the chaos settles, leaving the submarine enclosed in a crystal of ice.

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Texture, taste and composition

Abyssian water has a teal tint and a weak bitter taste. It lacks all the beneficial minerals and nutrients that Dunian water has and while it can be drunk, it does more harm than good. With its lack of beneficial chemicals, it will pull nutrients, salt and minerals out of the body through osmosis, leaving it in a dangerously unbalanced state. It contains a plethora of foreign substances, likely from abyssian volcano eruptions, that can be harmful to ingest.


While fatally freezing in most places, in some locations near and on certain floating islands, heavy volcanic activity heats the water to high temperatures instead, causing strong currents when the hot and cold waters meet. These currents are treacherous and can easily throw a navigator completely off course. With the lack of any useful, central navigation system, this can spell doom for the ship. The intense cold of the Abyss also pose a hypothermia hazard for both bases and submarines. Careful engineering must be done to ensure things don't break or people freeze to death.

Bottomless, endless

No bottom or surface has been found in the Abyss and the lack of an increasing pressure shows that the Abyss lacks gravity to compress the water. There are currents and bubbles left in the water drift with the currents rather than rising towards a surface. The bubbles will eventually destabilise and dilute with the water.

The Drifting Islands

There are millions upon millions upon billions of floating islands, like Dunia, scattered throughout the endless Abyss. Some are as large, or even larger, than Dunia. The vast majority are small islets that can still be several thousand kilometers across, akin to asteroids in our own solar system. These islets can be rich in resources and make for attractive mining sites for a modern society capable of exploring the Abyss. Because of this, in the more modern times in Dunia's existance, prospecting and mining base establishment was rampant throughout the Abyss.

The Absolute Plane

These islands all have the same gravity as Dunia, pointing roughly perpendicular to the island's surface, giving the Abyss an absolute horizontal plane of reference. This gravity is non-uniform and confined to the islands themselves, fading to near nothing only a few hundred kilometers away. Peculiarly, this gravity is uniform on the surface of the island, but once off the surface, it gradually shifts angle to point towards the rough center of mass of the island.

Navigational Hazards

The vast majority of floating islands are very small, barely larger than a few kilometers across. These small islands are called islets and while they are rich in resources, they present a serious navigation hazard for primitive submarines relying on SONAR alone.

Worse yet, the floating islands that dot the Abyss are all free-floating in the inky blackness, which means they will drift with currents and change location. On the macro scale, these movements are small and lethargic, but they are enough to put early colonies in danger of drifting out of supply and communication range. Even worse; they constitute a fatal navigation challenge for those traversing the Abyss since they can't be reliably mapped.

Abyss gate technology

The Abyss Gate was invented some time prior to the Cataclysm and has served the Dunians as their one gateway to the Abyss. It is a huge, circular airlock coupled to a supersized subharmonic resonator. Once the airlock is sealed and a 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. Over time, this technology was improved upon. Initially, it fully phase-shifted the entire dome inside the gate, leading to a violent inflow of Abyssian water. This occasionally led to equipment and personnel damage. At its peak, the Abyss gate could modulate the phase, leading a much smoother filling of the cavity, reducing risk.

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.

Lost Colonies

Colonisation and exploitation of the Abyss started almost a century before the Cataclysm with hundreds of established colonies throughout the ever-expanding influence of Dunia in the Abyss. However, with the Cataclysm, the vast majority of governments and corporations managing these colonies were destroyed. Suddenly without either communication with or supplies from Dunia they found themselves isolated and left to survive on their own.

With locations of colonies being a closely guarded secret among corporations, there was no way for the reeling survivorsto even begin thinking of saving these colonists. The vast majority of established outposts and colonies died out within seven months to a year following the Cataclysm, due to lack of supplies and maintenance. Exceptionally few miraculously survived through ingenuity and design, but especially the older outposts were not designed to survive in isolation and lacked the ability to generate oxygen, food and drinkable water in suffifient quantities to survive for too long without relief.

Many, many of those colonies went under either through starvation, lack of maintenance or just madness. Lost in the darkness forever, having drifted far out of supply and communication range and lacking food and water, making them dark, deserted tombs. Their ruins now litter the Abyss. A testament to the Dunian's progress and failure.

Traversing the Abyss

With its extreme cold, pitch blackness and great distances, travel in the Abyss has always been difficult and dangerous. There is no all encompassing GPS system, no permanent landmarks or lights to guide you. Just knowing what is the universal "up" and "down" is a challenge when you're lost in the inky blackness of the Abyss.

Inertial Navigation

In medieval times, navigation was done largely with the help of the sun, but since it was only up during the day, there was a real risk of becoming lost during the night. In more modern days, ships, airplanes and submarines navigated Dunia with the help of Inertial Navigation Systems [INS]. INS are dead-reckoning systems that use information from previous determined locations, inputs from gyroscopes and accelerometers and complex computers to calculate where you are. Using the sensors to track in which direction you have moved and for how long, you can calculate with decent accuracy where you are.

Dead-reckoning systems are inherently plagued by cumulative errors as there is no way for the system to self-correct. With the relatively small distances traveling across Dunia, INS have been accurate enough to get anyone wherever they need to go safely. Especially with direct communication of land-based navigation stations helping to realign INS on the fly.

Circumventing Unreliability

INS, no matter how accurate, are too unreliable to function over abyssian distances due to the cumulative error margin and in order to remain safe, they must frequently be realigned. This puts a hazy, but ultimately absolute, limit on how far you can safely travel with INS. At the peak of abyssian exploration, about a hundred years following the Cataclsm, most manufacturers recommended a realign every 6 to 12 hours. You could technically go for 12-20 hours and still be reasonably accurate within a kilometer of your destination. But when it comes to narrowly navigating a debris-field or an islet cluster, you need more accuracy than that or risk becoming another wreckage floating in the inky black.

Over centuries, countless vessels have been lost due to navigation errors, crashing into an islet or getting lost in the darkness. Even when stretching the reliability of INS, you wouldn't get far in the Abyss due to the extreme distances.

The Bouy Network

To combat the inherent limitation of the INS technology, the Abyssian Bouy Network was invented. The ABN was a series of sophisticated and expensive probes that interconnected to each other via hypersonar and used their relative locations to adjust their position in the Abyss, allowing them to remain stationary relative to Dunia. Vessels could approach these bouys and realign their INS with the position reported by the bouy and thus extend their operational distance. The ABN also allowed communication requests to be sent and received while linked to a bouy. A submarine vessel's own hypersonar transmitters were far too weak to bridge the immense vastness of the Abyss and they had to rely on the ABN for relaying messages to Dunia, colonies or other vessels. Without the ABN, a submarine was blind, deaf and lost within a day.

The ABN allowed exploration further and further into the Abyss. A sort of creeping boundary for Abyss travel, stretching ever further into the blackness like narrow highways into the unknown.

High Frequency Mapping

To avoid crashing into other vessels, islets and other floating debris, abyssian vessels were equipped not only with strong passive and active low-frequency SONAR but also a high-resolution, high-frequency sonar that used ultrasound frequencies to build a coarse image from the reflected sound waves. HFS or HF SONAR was used primarily in dense islet clusters and other areas where collision is a risk. These HF SONAR arrays improved with time and could eventually display a fairly detailed 3D image of the surrounding space around a vehicle, obviously without color, as it relied on reflected sound.


There is plenty of flora living in the Abyss but animal life is sparse. There are microscopic plankton living in the waters and the occasional jellyfish-like creatures that float about, but they tend to stick close to floating islands with volcanic activity, where the waters are warmer. Abundant animal life is found far from Dunia, near particularly active volcanic regions. By the time of the Cataclysm, the Dunians had not discovered such a place.

They, of course, had rumours and stories of colossal monstrosities floating through the depths and several hard-to-interpret SONAR logs, but no substantial evidence of such things. In most cases, the logs have been easily dismissed as detected landmasses, rather than anything living. But the rumours persisted and the prospect of enormous aquatic monsters made for great storytelling. The entertainment industry in Fusion City went absolutely wild with it.

The Leviathans

Vast leviathans do live in the Abyss, however. They stay near areas with abundant other aquatic life and feed upon them. Many of these enormous creatures dwarf the largest submarine ever invisioned by the Dunians, and can spend centuries in a hibernated state, just drifting through the Abyss. Many feed on a combination of large, complex life-forms and plankton. Most sustain their existance by consuming thousands of tonnes of plankton each day, just drifting near volcanic islands and islets.

Should the Dunians ever encounter these huge leviathan creatures, the colossi of the Shadowmark would appear as nothing but a nuisance by comparison.

Cover image: Atlas/Beluga Concept by Unknown Worlds


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16 Dec, 2020 16:15

I love that your world's version of space is a vast ocean, though not an ocean that could ever be found on earth. The thought of the leviathans lurking in the darkness is terrifying, even if they do just eat plankton.   Near the beginning you mention that they found out 'relatively soon' that the world was flat - did you mean 'recently' or did you mean 'early in their history'?   Great article :D

16 Dec, 2020 16:53

I should probably clarify that one, yes. It's not exactly "caveman" early, but it is in the middle of their "middle" ages, more or less. Hrmm...I'll think about this one. It can be worded better. Thanks for pointing that out!

Author of prize-winning RPG settings Dark Shadows and Cinders of the Cataclysm. Designer of the narratively focused CD10.
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