Visit Liberty City When you want:
This trick requires a Gameshark, Codebreaker or ActionReplay with the code: "Walk/drive through most walls." enabled.
Head over to the Gym in Los Santos. (Ganton Gym.) Move over to the punching bags on your left. Go to the second one and face the wall behind it. Enable the "Spawn Jetpack" code. Go to the map screen and place a marker (Press circle.) on the following location: East beach, in the middle of the highway, parallel to where the racing track is found. Now it is time to use your jetpack. (If you have done all the other things correctly.) Boost upwards, then hold R2 or L2 to Strafe-jet to your location. Once you are near the marker, land. You should see a yellow marker. Get off your jetpack and enter it. You are now in a part of Liberty City. Then, go to your map again and mark the following location: Vinewood, slightly above and to the left of the middle-left corner of the big and triangular-shaped structure. Fly there. this is going to take much longer, but when you do, you will see the familiar streets of Liberty City.