Thanks for all the help guys!
In the end it was the forced perspective idea that turned out to be the easiest method and it worked awesomely!
What I did was at the bottom I cloned the textures and dragged them down angling them as I went, which wasn't all that much as I am working with Blackreach walls.
What that allowed was for the bottom textures to blend in with each other at the bottom.
Doing it this way allowed a few things to happen "naturally".
The built-in FOV fog makes it so you can't see where the textures touch, thereby the depth is "limitless".
Since the textures touch it released me from having to make a "kill box" and the player will die if they fall/jump.....eventually

I did almost the same thing for the ceiling, where I cloned and brought the walls up and angled them. I used a ceiling tile from Blackreach way up high and when it was done it looks as high as it is deep!
Thank you all very much!