Black-Ceilings
From MapSpawn
Black ceilings effect, oldschool like in perfect dark and half-life
Valve once said nobody will look up. Since they've said that, I have always looked up.
Black ceilings are clever abstractions of reality, seen in many games in the early days. Less is more sometimes, and black ceilings and even black pits are a very compelling and efficient way to convey mystery.
Blackness and diametrically whiteness are interesting ideas to say there is more without showing more. A transpositioning of foreshadowing from literally works.
Unreachable player zone, player cannot touch these things or it breaks the effect.