"bottomless pit" effect?

Let me say first that I have no idea if this is in the right section. Anyways, in an animation I plan on making the character will look down a long elevator shaft. The elevator shaft will go so far down that you can see the four walls closing in on the vanishing point of the scene ,or you will see mist showing how far down it is ( it will also get darker and darker.), but I have tried both these effects on the scene. The mist did not work because I am using an ambient occlusion of .007. I cant get rid of the ambient occlusion because it helps get the exact lighting i’m looking for. Trying to scale the walls on the Z axis did not work because I would have to scale them so much that my computer would actually start lagging so bad that I couldn’t render a single image, and scaling in loop cuts along the elevator shaft as it went down would not work because it looks blatantly obvious the elevator shaft is being scaled in and it doesn’t give me the effect i’m looking for. Is there any other way to get a “bottomless pit” effect on this scene I have? I hope I explained that well enough.
Thank you for your time.

maybe you can post a picture of your results, then we might be able to find some work arounds or solutions.

If it actually is an elevator shaft, maybe just model what it should look like on the one floor below the one your character is on and use the array modifier to repeat your shaft downwards for as many floors as it takes to vanish? If lagging is just an issue in the viewport you could then turn the modifier off until render time.