I tried to find the hidden version of Liberty City in GTA SanAndreas today.
First I went to the city of San Fierro in order to stash an airplane and a motercycle, as they were crucial in my efforts.
Then I went to the gym in Los Santos. A few cheat codes later I have a full set of weapons and a jetpack. I proceeded to kill everyone in the gym, because for some reason the glitch only works if you do that. Afterward, I flew directly up. The ceiling wasn't solid, so i could just go through. I then flew across the invisible countryside, as i was not in the same planes of existence as the rest of the world anymore, and found a marker not too far away. It then took me to a half finished... club... In which I could walk through everything but the floor and walls. It was freaky. Then I flew some more and entered another marker. I ended up in a warehouse, which was, again, unfinished. After flying some more I found an entire neighborhood in San Fierro, fully intact. As it turns out, my airplane and motorcycle was still there. A few more cheats and some very complex manuevers and really really quick thumbs later, I was in the airplane which was hurtling away from the ground.
This is the part where i failed.
As it turns out, the entire city of San Fierro was still there, just invisible. I was off the ground for a full minute before hitting an invisible skyscraper (and wouldn't you know it, it also happened to be the one that was glitched and causes everlasting explosions). I jumped out of the airplane, which didnt do much good considering I was in a universe where everything was invisible. Also, I was really high up in the air and died from hitting the ground too hard.
And that is why I will never try that again.