system
Given the following post, respond as if you're commenting on Reddit:
human
[The Elder Scrolls] If I start at the surface of the planet and keep going up (levitation, rockets, big-ass ladder...), what will I encounter and what will happen to me?
gpt
You will eventually reach the "slipstream," which is the edge of reality between Mundus and the planes of Oblivion, and where the Battlespire was located.  From there, it seems to be easier to open a portal to Oblivion (they're much more common in that game than others), but opening a portal is still necessary to cross that final threshold into a totally different world.  Just continuing to go up doesn't seem to be effective.

It's not clear whether you'd hit a literal wall, or just kinda get lost in the aether though.