Generating walk-able looking space out of the bounds of the map?

What I’m trying to achieve is something like this. But say if I made a stencil on a wall that has nothing behind it, I want to make a small walkway or path behind there, as an illusion that there is something behind there, such as a corridor, instead of just black space. If its truly walk able it would be better. Any ideas on if this is possible?

Oh and also is it possible to make it so players able to pass through (stenciled) walls?

You can only make it visual using stencils. You can’t make it walkable.

you could fake it like gravity hull, i guess.