While the DARK•HERITAGE setting naturally gets the lion's share of attention on this site (given the site's name), I also have other projects and interests that I dabble in from time to time. One that's lingered for quite a long time in a parallel development path is the unnamed Pleistocene setting. Based on a similar idea to Robert E. Howard's Hyborian Age, it posits a mythic age prior to the launch of recorded history. Taking some paleo-historical/climatological data, combined with pseudo-science, I've been developing a setting that mimics superficially the Hyborian Age in many ways.
Geographically, I've set it up to be the Bølling-Allerød interstadial--about 14,600 years ago through about 12,800 years ago. The Bølling-Allerød was an inter-stadial period, i.e., a period of relative warmth and glacial retreat. It ended with the Younger Dryas--the prevailing theory is that as the Laurentide Ice Sheet continued to melt, an ice dam broke and the massive Lake Agassiz--containing more fresh water than all of the world's freshwater lakes today--flooded into the Arctic and North Atlantic Oceans, disrupting thermohalene circulation, and causing a pronounced cold spell (nicknamed the Big Freeze) which lasted for 1,000-1,300 years or so. (Technically, the Bølling and Allerød periods are two separate interstadials separated by the Older Dryas cold spell--according to some chronologies, at least. Others have them combined, with only two Dryas cold spells instead of three. I went for the simpler model.) This Big Freeze not only set in motion the extinction of much of the Pleistocene megafauna, resulting in the impoverished megafaunas we see today in most continents other than Africa and to some extend Asia, but triggered the advent of civilization as we know it. Reactions to the changing climate are hypothesized to have triggered the formation of agricultural civilizations (such as the Natufian culture of the Levant) from the hunter-gatherer civilizations that existed previously. From amongst these earliest agricultural civilizations later emerged the first recorded and historical civilizations--Sumer, Egypt, ancient China, etc. This is the stuff that's actually scientific, and forms the first leg of my three-legged High Concept chair.
The second leg comes from the best-selling, yet scientifically panned ideas of Graham Hancock, a Scottish pseudo-archaeologist who writes books about aliens building the face on Mars at Cydonia and stuff like that. Among his slightly more credible--yet still only marginally so--ideas include the notion of global Ice Age civilizations that were destroyed by rising sea levels, the notion of the sphinx being earlier than dated by contemporary Egyptologists (the water erosion hypothesis is actually supported by some pretty credible data, but Hancock has hijacked it into his theories, which doesn't help its believability, sadly) and other fringe ideas. He also has a number of catastrophic theories in print that would seem to contradict plate tectonics theory--but which you've gotta admit lead to some dramatic story potential.
Combining the first and second legs already gives you the potential to have something quite like the Hyborian Age. Taking cues from that, as well as other interests of mine like the Viking exploration of North America, I create the third leg--and the more overtly fantastic leg, wherein I utilize the Hyborian model to project transparently more modern cultures backwards in time to the Bølling-Allerød, "fantasy" them up a bit, and include such "classic" ideas as the lost continents of Atlantis, Mu and Lemuria. It's with this third leg that I abandon any claims to rigorousness to the real-life scientific leg of the chair, and admit that it's only a platform from which inspirational ideas are launched, at best.
In any case, I recently re-read Howard's famous historical essay, in which he placed the Hyborian Age in context with his prior Thurian Age, and the later historical ages, explaining in his alternate history where the Hyborian Age fits in. I'm working up my own similar essay, creating context for my own "Hyborian Age" which is, of course, not really what I'm going to call it. But this unnamed setting, which is much more overtly sword & sorcery influenced, and not at all unlike Howard's Conan series in terms of setting background (although more heavily focused on North America rather than Europe and the Near East, and more heavily featuring the wild animals of the time as a recurring plot element). This separates it thematically a fair bit from DARK•HERITAGE, but hey, that's why it's a separate setting after all.
I've included some art from Ka-Zar, a Marvel Comics character who's kind of like a Tarzan analog, except in the Savage Land, so he was raised by a sabertooth and fights dinosaurs and stuff. It's a weird conceit in some ways, while in other ways, it's the best picture I could find to illustrate my setting as I envision it.