Dentrissa, the Twisted City

Once a flourishing elven settlement, the city of Dentrissa fell prey to the largest supernatural disturbance in known Continental history. Being plunged into the darkness of a different reality, the city and its inhabitants vanished one day, leaving their former homeland a cursed, darkened land of danger and monsters, stalking whoever crossed into their territory, and sometimes venturing beyond it themselves. Then, years later on an another unremarkable day, the city reappeared, twisted and strange, inhabited by people that looked nothing like those that lived there before and a mentality and culture that would baffle and intimidate everyone else on the Continent in equal measure to this day.

History

Dentrissa was once a major city of the elven kingdom of Elverith, located in the western part of the continent, nestled in the eastern face of the Morhanth mountain range. Prosperous and beautiful, the city flourished, its streets full of traders, artisans and citizens, all contributing to the lively and colorful atmosphere, saturated by the smell of great cuisine and lead by a council of learned magi and scholars, as well as benevolent aristocracy.
One day, however, the city was taken by a strange sense of unease and mounting darkness that nobody could explain. This foreboding atmosphere would keep getting worse and worse from then on, compelling many to leave the city, whilst most of the others turned to their community leaders for a solution. But not even the renowned magi of the Dentrissan Academy could as much as guess the reason behind the strange happenings. It would not be long, however, that the question itself would become irrelevant.
After two weeks of this unexplainable crisis, a much more shocking and otherworldly event would change the city's history forever. About an hour after noon, the city, now gripped by an atmosphere so tense it was nearly unbearable, vanished from existence. By the pieced-together recollection of eyewitnesses, all of whom turned insane from witnessing the event, the city suddenly started bending in ways it shouldn't have been able to and collapse in on itself, dragging and stretching the countryside with it, until it dramatically collapsed into nothingness and the stretched out surroundings returned to their original state, releasing a shockwave of what they described as "true wrong" that shook the world around it and filled it with a sense of dread and otherworldly unease.
These outside impressions, however, are nothing compared to what the people in the city experienced at the moment that would come to be known as the Worldshift - they would see their entire reality change around them, as everything they knew bent into bizarre shapes until it became a smear, their minds attacked by conditions that were never supposed to be experienced. Every single living thing lost consciousness or perished in the Worldshift, never experiencing the final collapse of their surroundings and its plunging into a dark, lightness reality, where it would start to normalize again, although in a new and unfamiliar form.
Those that woke up would see a terrifying and highly disturbing sight - their beloved city on a dark ground under a black, starless sky, only dimly lit by strange blueish lights supposedly hanging on trees all but invisible in the total darkness around the city. But Dentrissa itself would not survive the incident unscathed, either - most of the city was leveled, the masonry unable to withstand the extreme stress it was exposed to and what remained was often twisted into strange shapes and fused with other buildings, creating grotesque and seemingly impossible structures, rendering the city nearly uninhabitable. The citizens too were affected - most of them died during the event when everyone fell asleep, while many others died once the city crossed into this new, alien world of perpetual darkness - much like the buildings, there were numerous lifeless bodies and parts embedded in the walls of buildings, in the ground or in each other, falling prey to the chaotic forces that failed to return the city to its original state.

The former site of the city in Impera was an empty, lifeless place radiating dark, alien energies into its surroundings, twisting the forests and turning the fauna into strange monsters, active only under the darkness of night. Many magi an researchers would attempt to find an answer to this most shocking and disturbing of mysteries, but none would find one that would provide any proof to support it. Most learned men eventually surmised that the city was taken by the elven god of the underworld, Senthanel, as punishment for the sins of its citizens. And while this was not the work of any hateful god, their guess was not all that far from reality.
Whilst the reason for the Worldshift is unknown, one thing would become apparent to the dismayed citizens of the ruined settlement quite early - the world they now inhabited was the notorious and terrifying Galothris, also known as the Umbral realm. The old religions told stories of the realm of perpetual darkness and the realm of unending light that Impera was placed in between of by the gods, but no one ever believed that crossing the veil is possible. Having no choice but to adapt, the terrified citizens would learn how to survive in this new world, leading a difficult and extremely dangerous life full of wanting and struggle in the bowels of their ruined city.
Seventeen years have passed in Impera when a disturbing atmosphere suddenly took hold of the former site of the city. As soon as these news reached civilization, a large number of scholars and magi from all over the world flocked to the site to study the bizarre happenings and hopefully to resolve the mystery behind the city's disappearance. This time, they had to suffer only a week of increasing discomfort before a predictable, yet still surprising event occurred - Dentrissa, the Lost City, returned to its original reality, smaller, twisted, ruined and rebuilt to the point of being nothing like the city it once was. The white marble of its walls was now black, unseemly stone blocks, the fine golden and silver ornaments were all gone, with only crude stone statues of otherworldly horrors and monsters resembling the ones the city left in the wake of its disappearance adorning the masonry; the majestic roofs of fine wood and colorful roof tiles coated in shiny lacquer were now scraggy roofs of broken and dirty tiles and rotten wood, often broken to the point where they exposed the buildings' interior to the elements, yet only rarely patched by uneven wood planks.
Those observers that survived the return of the city with their minds intact and those that came after the reappearance, were faced not only by the strange and twisted architecture, but also by its denizens, who looked utterly alien as well, to the bafflement of the magi and the sorrow of relatives hoping to see their loved ones again after seventeen years. As a matter of fact, they recognized nobody in the city, despite most of the newcomers, extremely defensive and refusing to come out into the light, being clearly too old to have been born in the past seventeen years.
Eventually, the two sides met in a pitch-dark room at the edge of the city, in one of the many buildings ruined upon reentry into Impera. The magi realized that the Returned, as they would call them, were strikingly different to their native counterparts - their skin was extremely pale with a hint of grey instead of pink, their hair was white and of lower quality than is common for elvenkind and their eyes were quite large with the black irises taking up almost all of the eyes' surface, showing only a little bit of white in the eye corners. Their stature was smaller than average and they appeared to be extremely averse to anything but a small amount of dim light.
Although speaking a very heavily modified version of the unified elven language and having an almost incomprehensible accent, the Imperans finally managed to establish diplomatic contact with these grim people, inquiring about their time away from Impera and presenting them their side of the events. While the Returned seemed to be unable to tell how long they have lived there, since without a day and night cycle the measuring of time was not only unnecessary, but downright impossible, they confirmed that they were descended from elves from this world, who, according to their spoken tradition, were transported into Galothris along with their city from a world of lushness, greenery and light. Upon further investigation it was revealed that nine generations of Returned passed since then, establishing that time can flow at different rates in different worlds.
Though slowly getting used to their new environment over generations and opening up to limited exchange of people, goods and knowledge with the rest of the world, the Returned, now commonly known as Dark elves, remain insular and distrustful of this alien world and the rest of Impera seems them through the same paranoiac lens, experiencing a range of emotions and opinions from a reserved curiosity to direct calls for genocide
Grim and self-centered, the Dark elves are content to be left to their own devices in their city and surrounding domain, cursed and transformed into a land vaguely reminiscent of their homeland. Obscuring their domain in a magical black fog, the twisted spires of the once radiant Dentrissa are the only things that poke out from the darkness that perpetually covers the home of the mysterious and feared Dark elves.