If you go to coordinates X 316.8 Y 422.2 on the map, you'll find a ladder. While going down the ladder, and doing the quick slide down animation, keep holding down and you'll slide right under the world and into white space. All you do is free fall forever, but you can use the wings suit. Also, I somehow landed in water on my first time which ended up getting me 2 trophies for "free fall" and "fearless or stupid".
Not sure if it's already been found, and I would like confirmation that someone else can do it. I've done it 6+ times, and works every time. Caution, there is no way out other than to "fast travel".