The flying tank.
Get the Rhino tank, and then put the dodo cheat on. Then go find a long strip on land, an then aim the gun backwards and fire! Keep firing until the tank takes off. By doing this, you can go higher than helicopters and planes, and reach the highest building in the game. Note: Try not to land on it, you'll just fall through.
We have more cheats and tips for this game here, Grand Theft Auto: Vice City cheats
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