And, for ease of reference, here's the original setting description:
One thousand, three hundred, and seventeen years ago, the legendary spark Leonard De Quirm, constructed the Nexus, also known as the Great Clock. It linked, and more importantly synchronized hundreds of realms. No longer did trading expeditions randomly vanish years into the future; sparks from the connected realms could work together without discovering that their partner had died of old age overnight. The golden age of knowledge had begun.
However, all was not entirely well with this golden age (surprise, surprise). The Nexus is a horrifyingly complex device, and only Leonard himself understood the full reach of its workings. After his death, the sparks of the golden realms maintained it as best they could - but it was not enough. In time, dark cracks appeared in the paths between the realms, and beasts of pure shadow stalked the nights and brought death to the unwary. Dire cults sprang up, worshiping the darkness. Entire realms splintered away from the core, were engulfed in shadows, and lost forever. Many put their faith in the Clock, claiming that Leonard's greatest creation would, in time, re-align itself and return the golden age. It took one visionary hero, Othar Tryggvassen, to realize what had to be done: The Nexus had to be shut down; the Great Clock had to be stopped. And thus began the Great War; loyalists against time-shatterers against the cults of night.
No-one is quite sure what happened in the end; the realms that form the Core today were cut off from the Nexus prior to whatever Othar did within its workings, and the known worlds lapsed into barbarism for half a thousand years. This, however, is known: While the Nexus may have been disconnected, the Clock at its heart never stopped; it merely lay dormant until its rediscovery and partial repair by Oberon, three hundred years ago. Six realms now form the Core; each linked to the Nexus and loosely synchronized. Oberon claims that the original designs' perfect lock-step is what caused the problems, and that no new shadows will leak in from the gaps between the worlds. So far, he seems to be right - though the cults of darkness still lurk with whatever shadow-beasts yet exist.
The realms of the core are these:
1) Astaria, The Golden Fields - an idyllic land of rolling plains and towering castles. Originally plagued by clockwork giants left over from the Great War, but most of these have been shut down by Oberon. Astaria, and by extension its inhabitants, are generally considered to be fairly boring. Useful (most of the food supplies of the core realms are grown here), dependable, but boring.
2) Irallith, The Realm of Wind - Airships perpetually roam the skies of this realm; the Great War left a poisonous black cloud upon the land. No-one visits the darkness beneath - save only the mad junk divers, and they are becoming increasingly rare now that Oberon has opened trade with other realms and the floating cities no longer need spare parts and raw materials scavenged from beneath the clouds.
3) Tulthin, The Great Machine - This realm contains a continent-wide device, most of it clearly broken and inactive. Few people live here by choice, but the realm is important as a source of pre-made parts and rare metals. Many people believe that this realm is somehow related to the Nexus.
4) Chalkon, Land of the Talon - Chalkon is a land of dense jungles, giant lizards, and ornate pyramid cities. Many of the natives have been altered to be faster and stronger than a normal human, taking on some aspect of one totem animal or another. Most notable of these are the jaguar princes - local nobility who chafe under the outside rule of Oberon. Unsurprisingly, Chalkon's specialty is biotechnology - strange drugs and medicines, and even expensive processes to offer totemic power to those not born with it (though the esteemed jaguar bloodline is never made available for mere monetary payment).
5) Stygia, The Underdark - Much like Irallith, the surface of this realm was rendered uninhabitable during the Great War. Its inhabitants now live in a massive network of caves (some natural, some artificial), or in submarines and underwater cities beneath the seas of the realm. Strength is the most valued attribute here; strength of construction; personal strength and endurance. Buildings within the larger caverns look more like bunkers than anything else; they are, after all, built to survive even the most violent of cave-ins.
6) Eleghost, The Blasted Waste - Nobody is quite sure why Oberon connected this realm to the Nexus. Massive craters dominate its landscape, and only shattered scraps remain of what must once have been great cities. Perhaps its purpose is to serve as a training ground for Oberon's armies; the place certainly has enough dangerous mutant creatures and still active war machines...
And then, of course, there's the Nexus itself; a gleaming metal palace with permanent gates to each of the six core realms, and a vast array of secondary gates that are only opened as requested by traders and travelers... or never opened at all. The nexus is entirely indoors; though it contains parks and open spaces, there are no windows to the outside, nor any signs of what might lie beyond its borders. This is Oberon's personal domain; the guards are competent, and do not allow curious sparks to explore where they ought not to be.
Beyond these six (seven? six and a half?) core realms lie a multitude of other places, reachable by temporary portals within the Nexus, or gate drives, or teleportation systems, or any of a variety of other strange devices.