Grand Theft Auto: Vice City Stories Cheats :
You go to one of the bottom two bridges (cant remember which), starting from the left side of the map. jump in the water and swim to the other side of the bottom of the bridge. there is a ledge to climb up onto, but you cant fit in the space above. keep climbing up until you get stuck there with your head in the bridge. keep moving and jumping until you end up under the bridge, where you can look up and see the people and cars above you!!! you can only kill people with a flamethrower. to get out go to one of the ends of the bridge and jump out. one hole to get out leads outside the bridge, while one leads to under the land where, if you swim out too far you start to "fall". everything gets blurry, unless you pause it, in which case the entire background is black. but anyway, you keep falling until you land on top of the land above you.