I was thinking of a world with a closed 3-dimensional space that would loop on itself. To describe it in another way: Forever traveling west, you came back to your starting point from east, same thing going south and north and forever. More importantly : digging the ground, you would end up falling from the sky.
To keep it simple, let's assume this universe is a cube. And Day/Night cycles, Seasons cycles would still be almost the same (even though I don't really know how it would work)
EDIT : Talking about scale of this universe, i would say something like 40,075km a side. I also forgot to mention that it would be a flat "earth" with a ceiling. (which would the same object as the ground).
How would that affect history, civilizations, religions, fauna, flora and physics in general ?
I'm not into reality-check, so please do not answer "It's impossible".