Based on the rolls we used to define our starting hex, I've fleshed out the background of our starting environment. Notice that this is pretty much straight out of the rolls with minimal editing to flesh this out and make it a (hopefully) enjoyable read. Seriously, AD&D DMG Appendices are content creation machines! Enjoy...

Eternal Valthrun, the Obsidian Citadel of the Cold Wastes, World's End, the Portal to the Dark - The City has many names and countless stories told about it for as long as men have told tales. Ancient beyond memory, the city has stood in the wind-blasted steppes of the north for countless eons and has served as the hub of communication and trade between the rich demon cursed holds of the Inhumans to the north and the Realms of Man to the south. All manner of goods, both fantastic and mundane, flow in both directions through its cyclopean black walls. Some say the Men that currently are merely the latest upstarts to think they rule its labyrinthine roads and age-darkened halls, others say the Inhumans abandoned it after seizing it from its prehuman creators, but the truth is nobody knows who built the city or when it was founded. Although there are numerous remnants of previous civilization, both familiar and not, surrounding and beneath the steppes around Valthrun, none have yet revealed any cultural, architectural or historical connections to The Obsidian Citadel.
Valthrun is a city of narrow roads, steep windowless buildings, and iron doors protected (some say imprisoned) by 20ft thick black stone walls that rise unbroken to heights of 75 feet and surround the city of 40,000 souls. Its physical properties are a mystery. The stone used in its construction is unlike any that naturally occurs within a thousand miles around The City, and sages have yet to discover its like anywhere in the Known Realms. If the Inhumans know anything of its source or how it was so expertly worked, they do not speak of it to the humans. The avaricious dwarves speak with grudging admiration of the great artifice shown in its construction. The decadent and degenerate elves say nothing of it, too concerned with their relentless pursuit of unfettered hedonism. The insane gnomes, in rare moments of lucidity between their madness-inducing narcotic journeys to the Outer Dark, admire the supreme skill of the creators but quickly degenerate into ravings about the Horrors that were and will be again. The halflings? No sane Man would willingly risk life, limb and soul by deigning to speak with these naked cannibal savages to see if they even possess enough lucidity to converse naturally.
The buildings and their architecture are unique, sharing no commonality of culture or aesthetic with any other civilizations in the Realms of Man. All are made of the same dark stone as the city walls and are protected by 1ft thick wooden doors that never seem to rot, or need repairs. Visitors find the doors to be extremely unsettling - are they meant to keep the threats out or to trap the inhabitants within? There are no windows on the ground floor of any building in The City and are only seen on the upper stories. This, coupled with the narrow winding streets, turns Valthrun into a trackless maze for the numerous visitors, most of whom wisely pay local guides to escort them through The City as they conduct their business.
For it is business that is the lifeblood of the city. The City is the nexus of numerous trade routes among the Known Realms and the ancient cities of the inhuman empires. While various groups may be bitter genocidal enemies outside the black walls of Valthrun, all observe a truce while within its environs and those that do not, quietly disappear leaving behind the bloody rags of their once fine clothes as the only testament to their miserable existence.
Valthrun has a functional government ostensibly headed by Lord Jirex, Guardian of Portal. The real power lies with two radically different patrons: Kirenos, the Master of the Thieves Guild and Bilious Yarena, a Night Hag from the depths of Hades. Jirex, in reality, is largely a figurehead put in place by Kirenos and has no real power beyond the administration of quotidian affairs (such as city patrols, tariffs and the like). Jirex is, of course, well compensated for his role and sees little point in upsetting an eminently agreeable situation.
Little is known of Bilious Yarena since she (it?) takes great pains to ensure no mortal knows of her existence, goals or agents. Based on scattered records recovered from the Cold Wastes and other places, she has been part of the city for at least 1,000 years and quite possibly more. There have only been a few confirmed sightings of the foul hag in this vast period, and she has largely remained invisible, pursuing whatever her goals may be. She always operates through a vast network of operatives, only some of whom know their true employer, and has, so far, never interfered in the mortal affairs of Valthrun (at least far as anyone can determine).
Only slightly more is known about Kirenos, for he too prefers to keep a low profile. Nobody knows for certain his age or appearance, but all are aware that he will do anything to ensure the flow of trade is never disrupted and that every merchant pays their tax to him. If some choice items disappear, well, that's the price of business in The City.
The most famous site of numerous ruins scattered the Cold Wastes surrounding Valthrun is the Shrine of Lethria, some mile or so beyond the walls. Numerous adventurers have journeyed to the Shrine and explored its eerie depths, but very, very few have ever returned. Who can say if these poor souls met their doom in the Shrine's twisted depths or rather fell to the hill giants or leucrotta herds that roam the Wastes? The handful of brazen fools that have survived and returned did so with great wealth and doubtlessly fabricated tales of horrid undead and twisted dimensions that nearly broke their sanity.