The thing starts around 0:10 of the video. I somehow ended up in the Red Cave (I was in Red Yard).
Hey Ing JoRu.
I looked at your clip and loaded up Antifreeze in a custom game to see if there was an issue with geometry. However, it looks like there is simply a small gap in the ground that players can simply use to drop down to the lower level.
Here’s an image of what the hole looks like: http://i.imgur.com/ePp48iK.jpg
