Imagine, if you will, that Isaac Newton was wrong about gravity.
That string theory wasn't quite it.
That theories such as warped passage and field of force gravity were the correct ideas, that the idea of tesseracts was a viable and physical truth, and, of course, that the apocalypse was a long time ago indeed.
What's left after a sort of nuclear winter is a land that is inhabitable by any oxygen-breathing species, but isn't by anything anyone has ever seen before.
There are no people there, but the land wants people, and it uses its ways to get them -- so anyone, anywhere, in any possible plane of existence, in any version of any world at any time, has an equal chance of succumbing to what is really just a chance of bad luck and bad timing.
(That's a theory, anyway.)
Tesseract-like vortexes appear in lurking darks, and anyone who's lucky-or-unlucky enough to turn around an unlit corner at the specific time of one appearing is sucked in, and there's no way to go back.
Trapped in someplace that hasn't seen civilization in a long, long time, with no supplies, and no life besides the other stranded and whatever was there to begin with.
It's going to be a long ride.
This RPG is for fun, not for copyright infringement. Your moderators, if you choose to accept them (not that there is, unfortunately, an option) are metaphor, buongiornodaisy and innerbrat. They are reasonable and fun-loving people. Talk to them if you need them.