That's one of this other worlds: a Counter Earth, following the bold tradition of John Norman's planet Gor, but in a modest way.
You know how in this stories characters usually go, have their adventures, and them come back so they can share their amazement with the mundane; even if they may eventually find their way back to the other side of the mirror later? We have no room for the last part of it here. There is no coming back from Sharitarn: "The end of the Sewer" is how some iis (involuntary immigrants) affectionately call their adoptive world.
What they mean to say by the expression is that the Vortex transports people from parallel planets to Sharitarn, it does not works in the opposite direction. And nothing else do. Once in this Universe the only way out is through non-existence.
The Mage's Brotherhood is the only global authority on Sharitarn, and they only enforce one rule: the Exclusion Law.
"No Technology brought from the Vortex after the Age of Spiders can be tolerated"Bellow that level, civilization is organized in sovereign State Cities. The tools and constructions remind Earth Bronze Age, mostly. Whit exotic materials of countless different Universes that not always obey the same principles of nature, and also ostensible magic. Countless non-humans share that world, more species than we could register, but humanity is by far the dominant race now. Most humans don't like non-humans much, and they do have their reasons, not always perfect are those reasons but not always bad either. You find a Caste System among humans, adopted over the Ages by most other species how have to deal with ours. Also, you do find slaves everywhere. Mostly slave women. All free men carry a weapon, all the time. Never leave home without it. Duels are a normal way to solve controversies between adult free men, and they don't necessarily end in death but that possibility is always on the table. Honor and friendship have precedence over survival in the minds of common men. And keep a good reputation is as vital to survival as breath for most, what makes even the most pusillanimous spirit walk strait and hold his ground in public contexts. Did I mention that all free men do carry weapons? Yes, they do except for the mages. The use of shields and armours is restricted to few, curiously. Inside most cities only local Warrior Caste men and sigraxes can use those means of defense.