A very long time ago, a prehuman race coming out of the vast reaches of space established an outpost on Nardhome, in the center of a vast crater in the interior. There, they created a portal network connecting different worlds which focused vast energies into a location which I will call the "God Chamber" - named this way because its intended goal was to turn a mortal being into a god. They succeeded in their goal, but at a terrible price - the resulting god was Tekel, the God of Fear (and possibly the oldest God of Urbis), and the resulting psychic backlash killed all of their race on all of the worlds currently connected to the portal network, as well as damaging their machinery.
However, their machinery was so advanced that it was self-repairing, and over the course of eons the outpost slowly started to function again. Then explorers from the First City discovered this place, and after studying the site for decades they, too, attempted to turn one of their own into a God. But the resulting god was Nyros, the God of Diseases among other things, and while the resulting plagues might not be the main reason for the destruction of the First City, they certainly spelled the doom of the First City outposts on this continent.
Then the ancestors of the current Coastal Tribes arrived and settled this continent, building many cities. Their understanding of magic was not as great as that of the First City, so the purpose of the earlier ruins was not immediately apparent, though the danger of the fluctuating portals was, and so they built a great city to guard against the abominations that would emerge from the central crater from time to time. But eventually a powerful wizard arose from the natives who realized the true potential of the God Chamber, and he gathered his hordes of minions in the central crater while he studied the ruins for many decades. Eventually he thought he had learned what he needed and activated the God Chamber, but his understanding was incomplete and he became an entity of hunger and madness (the "father" of the wendigos and similar beings) short of a god. The excess energies went into his minions and spread across the land - the Great Scourge that killed most of the natives and forced the survivors to wait it out at sea.
But again, the prehuman machinery repaired itself, and just as the PCs arrive the ancient portals are beginning to flicker alive...
This backstory has numerous consequences for the campaign:
First of all, there are several sources of ruins / dungeons in the area. The Prehuman ruins will primarily be located in the far north, inside the crater (beyond the map I already posted), and will be the most dangerous - parallels to the Elder Things colony in Lovecraft's "At the Mountains of Madness" (and the "sequel" Call of Cthulhu campaign "Beyond the Mountains of Madness) are fully intended - though I don't plan on using Cthulhu Mythos entities directly.
The First City ruins will be more widespread, since they didn't initially come to Nardhome for the God Chamber - there may be abandoned mines, an old Hot Springs resort, research complexes, temples, and an old administrative center and the like. The PCs might also find abandoned and sealed complexes where the plague victims were thrown in - which might have been transformed into "ye liveliest awfuleness" since then (possibly Gibbering Mouthers?). Ultimately, these ruins will also be more "familiar" and understandable than the Prehuman civilization, since modern-day magitech is approaching that of the First City.
The Native Ruins will be more widespread still, and more recent, though culturally more alien to the PCs. They can range from small villages to entire cities, up to the Fortress City up in the North. They probably also include some sort of magics to prevent their destruction from the rather common earthquakes of the region, and they will likely be filled with all sorts of undead as well as spirits of hunger and madness - the remnants of the Great Scourge. Many of these ruins will be great "starter dungeons" for the PCs.
There will also be ongoing changes. First of all, the fluctuating portals will cause all sorts of alien creatures to show up in the north and gradually migrate south - the Surtus Termite being just one example. The PCs need to guard their fledgling colony against these new arrivals.
There are also a number of villains who will become aware of these ruins and - once they realize the potential of the God Chamber - will attempt to take control of it. The "ultimate villain" of the campaign will be the one who comes closest to accomplishing that, but any of these villains have a shot at it - this way the campaign arc can continue even if the PCs kill one of them. Possibilities include:
- The Worm That Walks - a Native sorcerer who turned himself into a living swarm of worms.
- A witches' coven from the Inland Tribes.
- A powerful priest of Nyros following in his deity's footsteps.
- The Athanatos Club, learning of a potent way of transcending human limitations.
- A rival city-state to Dartmouth, attempting to establish its own colony on Nardhome and trying to reach the God Chamber first.
Also note that for controlling the God Chamber it is not sufficient to be in possession of its physical location - it is also necessary to research the whole facility in detail, a process that will likely take many, many months even if the PCs get outside assistance (as they should). In Kingmaker game terms, whoever controls the site needs to erect a town with specialized research facilities there, and and only with such fully-staffed facilities will the meaning of the various pieces of machinery become clear. Then they also need to restore and control the counterpart facilities on the worlds reachable through the portals before they can actually power up the God Chamber itself.
If one of the villains controls the location, then that gives the PCs some time to try to wrest control from them. And if the PCs control it, the villains will of course attempt to do the same (not to mention steal their research notes). And once they fully understand what the God Chamber is capable of, they will have to wonder whether they should use it or not. Even without the God Chamber the location is still immensely valuable for the portal network alone, and understanding the magitech of the prehuman civilization will likewise boost human knowledge tremendously. But destroying the God Chamber permanently is difficult, and as long as it exist the powerful factions of the world will attempt to gain control of it...
So, what do you think of this outline?