Slipdoors are inversions in reality. A place where things on the outside are perverted on the inside. Anyone entering a slipdoor can expect to find a warped mirror image of what was outside the slipdoor.
Like the example I'm asking you about. It would most likely be a town. The slipdoor would ecompass the town, and maybe a little of the wilderness beyond, but not much more than that.
The world would look warped, like buldings, furniture, and trees that bent and angled in ways that almost make you sick to look at.
The sky looks like a gelatinous ever-shifting goo that constantly changes colors.
The people are the worst, though. They are warped beyond everything one can imagine. Every one is different, but mostly they look like someone pulled their legs inside out through their mouths. They are prisoners, created in the slipdoor to mimic someone on the other side. They die when their counterpart dies. They die when their counterpart leaves the area of reality the slipdoor mimicks.
The people of the slipdoors have minds of their own, as terrible as they are. And any would give anything to trade places with their counterparts in the real world.
The thing is: If one can leave the slipdoor, and put his counterpart in the slipdoor world, the slipdoor resident is free, while the real world person becomes his shadow in the Slipdoor.