Far below the effects of weather, tide, or current, the lost cities of the Tsithca'ca'dss hide in the endless night of the sea's most inaccessible depths. Ageless and unchanging, the decrepit remnants of these forgotten metropoli can sometimes be found by undersea explorers.

Wonderlands of inhuman conception, these cities are mazes of strangely organic towers and oddly-connected tunnels and chambers. The myriad grasping claws of the Trench Dwellers use any surface as a resting place, so passages and chambers are laid out with no regard for up, down, or other directions, winding in incomprehensible labyrinths.

The geometric concepts of the Trench Dwellers follow non-Euclidean concepts: surface dwellers exploring these bizarre cities often become disoriented, finding themselves in distant parts of the ruin without any sense of movement or transition. These rooms and tunnels were not built to provide shelter for the elements, so many are open to the sea, with large, oddly-placed 'windows'.

Blind and highly sensitive to sound, the Tsithca'ca'dss built their cities without regard to visual cues, but with careful attention to the acoustic properties of their shelters. Bizarre shapes fill the chambers, with no comprehensible function other than to serve as strange sound baffles and resonators. While many of these odd sculptures are shattered or warped, many of the intricate devices can be found intact in even the most decrepit ruins. These things emit a variety of odd noises, ranging from whistles resembling bird calls to low hissing sounds.

Stillminds
The most intricate of the surviving mechanisms of the Trench Dwellers resemble massive branching coral, with strange indentations covering them, indentations that match the underside of the many-legged Trench Dwellers. Revered as holy by the few remaining Tsithca'ca'dss, they call these devices ch'ip'quv, 'Stillminds'. Millennia ago, before their cities were half-buried ruins, the Tsithca'ca'dss used these items as a sort of 'mental amplifier'; large groups of the creatures would gather around them and be joined in a sort of mental communion, their intellectual abilities magnified immeasurably.

The Trench Dwellers often preferred to build their cities near vents at the bottom of the sea. The minerals and energy gathered from these volcanic rifts provided the alien creatures with raw materials and food for their lightless civilization.

Guardians of the Vents
In the heyday of the Trench Dweller civilization, they would surround volcanic heat sources with Khiop'rj v'no, vast arrays of strange organic mechanisms known to the merfolk as 'Colerids'. Resembling nothing so much as clusters of massive pipe coral, hundreds of these bizarre devices ambled slowly across the sea floor on small, clawed limbs that projected from their bases. They gathered the precious minerals released by the vents and excreted them in forms useful to their masters. In many places, the eons and the harsh environment of the volcanic vents have destroyed the alien biomechanisms, but in other areas, they have reproduced and proliferated.

Surviving Colerids are well-defended, having survived the eons protected by warlike biomechanisms known as 'Acanthids'. These spine-covered battle constructs are not particularly bright, but aggressively defend the items and areas placed in their charge. Maneuvering solely on sound, Acanthids charge toward intruders, rending them with their spined and bladed appendages. Those dependent on sight find them difficult to fight, as the biomecanisms often broject clouds of a black, inky substance when in battle.

Reaching for the Light: Outposts of the Tsithca'ca'dss
In a few places, the Trench Dwellers built outposts and strongholds far above the crushing depths that they favored. These were made for many purposes: Some were trade outposts, where members of that reclusive species would exchange items crafted with their incomprehensible technologies for items gathered by other species. Other structures were strange underwater fortresses, built to maintain the war machines that kept other races and the predators of the sea from troubling their cities in the trenches below.

Url'rroth, Place of the Darkhaunters
One of the more fearful legends of the Meremenne is the tale of an undersea fortress that they knew only as 'The Place of the Darkhaunters'. As the story is told, a migrant tribal school of merfolk was driven from their accustomed waters after a schism in their school. They settled in an area of rich fishing near the trench known as the Coelacanth Rift, where they dwelt for the better part of a season. Unfortunately, hunters from the tribe found a strange formation among the coral of a nearby reef, a sphere nearly a hundred fathoms in diameter. Although the discoverers of the strange formation were originally frightened by odd noises emitted by several formations next to dark openings into the sphere, they pressed on, exploring the winding passages and shadowy chambers of the interior.

Within, they found many things that they had never before encountered. Strange polypus growths, devices of gleaming materials they had never seen before, and small, noisy creatures resembling hermit crabs. All went well, until one of the creatures began to address them in the language of the merfolk, but with an archaic diction and phrasing they found hard to understand. The thing warned them that they had entered the seas of the Darkhaunter Culturals and would be required to hunt elsewhere. Filled with bravado, one of the merfolk warriors began to bluster about how his people would never be driven away. This was the last mistake he ever made. Devices that he hadn't even recognized as war machines swept forth from midnight-black corridors, decimating the hunting party in seconds.

The survivors fled back to their school's nest-site bare moments ahead of the things hunting them. Dozens of unheard-of devices swept in, crushing and rending the defenseless merfolk. Fleeing mermaids were shot down by spines launched incredible distances, while warriors, clumped together for defense, were blinded by projected clouds of inky darkness. In the end, only a bare handful survived.

Furious, the vengeful Sea-King of the merfolk led a retaliatory expedition to avenge the lost school. While the heavily-armed soldiers of the merfolk found a handful of alien machines (which they destroyed), none of the small crablike creatures remained at the stronghold. After they had finished off the stronghold's defenders, a monstrous war machine rose from the depths, dozens of fathoms across and nearly forty fathoms in length. Dozens of smaller constructs clung to its flanks, uttering warnings in unearthly, mechanical tones. They delivered an ultimatum to the Sea-King: Consider the spoils of the fortress as blood-price for the trespassing school of merfolk and molest the Darkhaunter Culturals no further... or be destroyed. Aware that a fight against such a behemoth would decimate his followers, he chose peace and survival. To this day, the people of the sea have avoided the Coelacanth Rift, where the Darkhaunter Culturals may yet dwell.

In other places, the millennia have wrought great changes in the seas. Areas that once were deep beneath the waves have risen near the sunlit shallows or have even been thrust above the ocean's surface. The Trench Dwellers that once inhabited these places generally abandon them when they near the surface, but other races are often eager to take over the ruins.

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