Say there is a physical end to this universe, and that we reach it. We bang on to some wall. What's beyond it?
Wouldn't that be part of the universe too? The point is its difficult to even visualize the physical end! Then is our universe a big loop of some kind? Does the space-time theory (which explains lot of strange characteristics of the universe) explain this in anyway?
I believe the universe is a 'closed' shape, meaning that there is no 'edge', however it does have a finite size. But just to entertain your question, if we one day did reach the End of the Universe we literally would be unable to describe anything on the other side.
Everything we know about physics, space time, the fundamental forces, the universal constants and so on only exist in this universe.
Anything 'outside' of the universe could potentially then have different laws of physics and thus would be completely beyond our comprehension.
Words would literally fail.