The Universe is a big place. Worlds, planes, realities - whatever you want to call them, there are uncountably vast quantities of them, almost as infinite in their variety as they are in number. Within a tiny fraction of these, quirks of fate, impossible coincidences and one-in-a-million chances have given rise to intelligent beings. Fractions once more of these beings rose to dominate their own worlds, and to begin to shape existence around them. Finally, on a proportion of these so small that it would be written off as a statistical anomaly were its effects not so profound, the denizens managed to break through the boundaries of their very world, spilling out into the multiverse, the pathways that lie between realities spreading out before them.
Some of these travellers blasted their way out with great magical rituals. Others constructed great machines to pull open the cracks in existence, allowing them to slip through. Deities empowered by the worship of millions declared “This is not enough”, and tore the sky asunder, fulfilling prophecies of promised lands and great catastrophes in equal measure. Many perished, or never return from their travels - thrust into dangers and threats more alien than they could possibly conceive, ensnared by temptations beyond their wildest dreams, or simply unable to replicate whatever feat allowed their passage in the first place.
A very few, however, survived, and many were infused with a hunger to push further afield, visiting more and more worlds. Their motivations differed - some wish to explore, to see what lay beyond the horizon of reality itself. Some sought to conquer, to extend whatever dominion they had wrought in their own world yet further. Some simply fled, their own reality being either too dangerous or too boring for them. Whatever their reasons, about three thousand years ago, this dimensional diaspora began to filter through the worlds of the multiverse. Some brought death and destruction with them, while others brought great prosperity and growth. Most of all, however, they brought one thing - the knowledge that something else was out there, and it could be reached.
Knowledge is power. It can also, however, be a burning hunger, and where these first travellers went, a desire to replicate their achievements and follow in their footsteps. As more and more strove towards it, dimensional travel gradually became, if not common, at least available to the upper echelons of society in many worlds, whether achieved within their own worlds, stolen from a visitor from elsewhere, or freely given by a charitable traveller. It has never been easy - no known method has been found that does not require immense effort in some shape or form, keeping its use sparing outside the rulers of the (exceptionally) few inter-dimensional empires that have been successfully established.
However, while travel between the dimensions remains difficult, communication turned out to be comparatively easy - still restricted to the most powerful mages and deities, or those in possession of significant technological or magical artifacts, but much less resource intensive once the threshold of capability is crossed. Thus, even in worlds where the power for a dimensional leap is still beyond imagining, the legacy of former travellers has often left a lingering awareness of the nature of the universe, and powerful individuals may still be in contact with their counterparts in other worlds. A certain community exists between the worlds, more often a sharing of secrets and fleeting conversations than actual meetings or visits, but a community none the less.
In such circumstances, knowledge flows. Wherever knowledge flows comes gossip, rumours, curiosities and whispers, especially in an infinitely varied universe. When an inter-planar traveller finds something of particular note, awareness of it tends to gradually filter out. It might be noted down in a hide bound tome passed down over generations by the descendants of a man who swears an angel fell to earth and told him great secrets. It might be the triumph of a budding telemancer, casting a scrying pool across the borders of worlds. The device built to listen to the heartbeat of the stars might reveal more than was bargained for. However it happens, when something of interest is found in the multiverse, sooner or later those of power find out about it.
Many of these mysteries are but fleeting, their secrets soon unravelled by dimensional scientists, burnished brass instruments reducing infinite wonder to a symposium paper. Others are destroyed by folly or art, the power to blast between worlds an unsafe thing in the hands of the clumsy or malevolent. Some, however, are destined to persist rather longer, enduring the probings and fumbling of those who inspect them. Some are artifacts that seem to violate the laws of the universe as understood by those who behold them. Others are sites that seem to defy explanation no matter how much analysis is cast upon them. While most eventually succumb to the weight of curiosity heaped upon them, many can remain unsolved for decades, some even centuries. There is one that has endured for even longer than that. Perhaps it is because of its scale - not merely a single object or locus, but an entire plane that seems to bend the rules as most know them. Perhaps it is because it is unusually resilient to scrying and magical communication, making it difficult for its denizens and visitors to relay knowledge to those without. More likely, however, it is because investigating it comes at such a terrible cost.
Around seven hundred years ago, interplanar travellers began to disappear. This went un-noticed at first - for even the most experienced, dimensional travel remains a difficult and dangerous process, and losses are always to be expected - their remains often found and noted by future explorers, or a lucky few of them re-emerging several years later, having finally extricated themselves from whatever ensnared them. However, the number of those missing began to creep up high enough that it began to be noticed - especially as no trace was found of any of them. Disappearances began to be investigated by those who counted the vanished as friends or acquaintances. Some of these parties found nothing, not surprising perhaps given the size of the Universe. More worryingly, however, some of these search parties, often the ones that had reported having found a trail, disappeared themselves. Quite a commotion arose among those aware of such things, along with mounting curiosity. After nearly twenty years of this, and many more missing, a message appeared from one of those thought lost. A warning.
Simultaneously appearing on the surface of every mirror in the glass city of Gathul, a face twisted by interference began to speak.
“Don’t follow us. We are trapped. We should never have come here”.
Many knew not what they saw, but a few understood, and the word began to spread. With this tenuous link, work was poured into making further contact with those presumed lost for good. Progress was slow at first, and some grew bored and arrogant, pronounced their intention to rescue those lost, and vanished as they had. The more patient, however, eventually managed to open a channel of communications. The effort required was immense, in excess of that normally required for several planar leaps, but words were finally exchanged with those lost, who turned out to be trapped within a rather singular world.
The story for all those there was the same. In whatever way was normal for them, they had mapped a route to this plane - some exploring blindly, some following the trail of lost friends, some curious as to why whatever normal method they used to scout ahead of their leaps seemed to be shorting out. They had made the jump with no particular difficulty, if anything finding it easier than normal. They had emerged among the ruins of a city whose architecture was unfamiliar - not an unusual experience, the trappings of dead civilisations often being found on planar travels. A cursory investigation by the first arrivals, who were motivated by scientific curiosity, suggested that there was enough of interest here to merit notifying colleagues and friends. Their normal methods of external communications failing (unusual, but not impossible amidst within a whole variety of strange conditions), they tried to leave the way they had come.
They found that they couldn’t. Nor could the next group who arrived, a pair of travelling knights-errant who sought to topple tyrants wherever they found them. The added efforts of the continued trickle of arrivals availed naught, and worse, some of the new arrivals were rather less peaceful than the initial hapless explorers. Division over the best way to attempt escape, and struggles over the limited comforts available in the dark, frequently rain-slicked streets of the dead city led to fractures forming within those forced to share community, and camps formed in various parts of the ruins, some relatively welcoming to outsiders, but others jealous in their protection of the place they had claimed for themselves. Several groups, upon realising that they were here for the long haul, turned some of their not inconsiderable power towards renovating a few of the buildings around them, and providing some limited luxury for themselves and their companions, when not turning their efforts to escape. The amount of time spent on this only increased as the sense of futility increased, some groups abandoning escape entirely, instead focusing on exploring and civilising the world around them. The extent of the ruins was vast however, and at this time there were still less than a hundred denizens of the plane. With the added difficulty of srcying and other methods of magical and technical exploration going haywire within the place, only small sections of the city were investigated, and smaller still built into something resembling a home within the grim place.
That was until the successful broadcast of the first message, achieved by a group quick to realise that with limited numbers working on the problem of escape, a solution was unlikely to be timely found. They were thus keen to broadcast their plight to those elsewhere, and to warn others away from the same fate. On the first point they can be considered to have succeeded. The latter, however, was not. The initial wave of explorers seeking to find and face the great danger more than tripled the population of the plane. This died down once more concrete communications were established and the precise nature of the danger publicised - not a great beast to be slain, or some wicked tyrant to topple but a seemingly inescapable imprisonment. While some did still travel to the plane with such an intent (often after declaring that they would be the one to solve what was fast becoming the most famous conundrum in the multiverse), the repeated failures of such endeavours quickly reduced their numbers. Indeed as more years passed, more and more people (not least many trapped within the plane) began to believe that no way out would ever be found for those imprisoned. Those outside thought of it as a curiosity, while those within redoubled their efforts to renovate their new (and presumably, eternal) home. The rate of arrivals to the plane dropped sharply, as who in their right minds, possessing the power to leap between the worlds themselves, would risk eternal imprisonment within one?
They did not, however, stop, as it turns out that some circumstances can make even an eternal prison seem an attractive choice, and others can make it not a choice at all. The most commom who chose to come to the plane were those fleeing from something. Often, it was justice - the power to leap between dimensions accruing disproportionally to those willing to indulge in a little tyranny and terrorizing. Standing atop the proverbial burning windmill, many a dark lord has chosen to make the jump to The City (as the plane has become commonly known, though it is far from its only name) rather than face justice, knowing that whatever force was hounding them would be insane to follow (though an unfortunate few foster sufficient hatred that their pursuers do). Conversely, a smaller number of brave heroes end up making the jump, whether seeking a safe place to lick their wounds after failing to defeat one of the aforementioned dark lords and certain that through the power of their righteousness and destiny will ensure they find a way out, or more cruelly, banished their by a sadistic opponent seeking for them a fate worse than mere death. Banishment is also used by some worlds as a punishment, using The City as a kind of prison for those to troublesome to kill or detain. And a very few still do turn up infused with scientific curiosity, convinced against all accumulated evidence that their must be a simple way out that everyone is missing.
Many of these powerful individuals bring others with them, whether henchmen, loyal retainers, incredibly unlucky graduate students, or in a few cases, denizens of entire villages when a departee has decided to go out with a bang. As The City’s population grew, and efforts to build civilisation upon the ruins redoubled, and as the years passed the majority of what had been found by the first arrivals (with the exception of the waterways, a convenient source of travel, irrigation and drinking water) was covered over with new edifices in a startling range of architectural styles. The small groups that had initially banded together for shelter and safety were the nexuses of these, development spreading out from where what they had at the time assumed to be their temporary homes had been built. As these expanded of course, they began to collide, merging to form larger clusters. Seven hundred years after the first travellers stumbled into it, The City would be almost unrecognisable to those few - a sprawling metropolis stretching far beyond the limits of the ruins, and hundreds of metres up into the ever dark skies. Populated by those whom fate has brought to its doorsteps (and their descendants), ruled and vied over by powerful guilds and organisations, The City remains to this day a prison, but one unlike any other that has ever been.