The Green wall is the largest of the known walls in The Outer Bubble. It is a large, flat wall of rocks that dramatically vary in size. It resides behind a smaller Blue wall. Space is bent in such a way around the wall that reaching it is impossible, as travelling towards the wall will move you away from it. This does not affect light for some reason.
How the Green wall came to be is currently unknown.
Gallery[]
The only real image of the green wall that isn't an estimation.