OK....I am limitted to 6 meg on my web site so I have remove the avi (Polygon.zip) and uploaded the level itself (Worlds.zip).
Use WORLDS.EXE to start the level.
Use Home for the engine speed.
Use key "A" to go forward.
Use key "C" to go backward.
Use the arrow keys for direction.
Hit F7 for First Person Mode.
Go under the prefabe in front of you and come up from below and hit against the horizontal platform.
The short canyon piece that I have is off to your left. It is big and brown so you can't miss it. In height stay a little above the height of the prefab and go towards the center of the canyon wall.
You do have to approach the wall but you need not get right up to it. Now look down toward the ground and you will see the transparent polygons. Now look up and let the canyon wall go down about half way on your screen and again you will see them suckers dissapear.
I have A4 version 4.23. I am using a slightly modified script that came with the flylevel. I have tried this on one other computer with the same results. The canyon model does have a very large polygon on the back side but that is not affecting the problem at hand because You will get the same results if you use a cube of 256 X 256 and scale it up somewhere around X40.
I did not have time to test the upload so if there is a problem I will have to fix it tomorrow when I get home. I hope that it is alright.
And thank you for all of your input. I do not post a problem unless I have tried everything that I can think of first.
I guess I better give you the link again.
http://home.earthlink.net/~ronholmes/
Ron