This is a fun glitch in Vice City and normally you would need to use the seaplane but here's an easy method I discovered. This was screenshotted on Android but I have tested it on Mac, Xbox, and iOS and it all works. Not sure about you PS3, PS2, Windows Desktop, and Windows phone users.
Step 1: Start at the First Safehouse
This is the Ocean View Hotel. Go to your bed and jump on it.
Step 2: More Jumping
From the bed, jump on the dresser and then on the wardrobe.
Step 3: One Last Jump... Be Careful!
This is very important. Jump off to here. DO NOT MOVE UNTIL YOU READ THE NEXT STEP.
Step 4: Go Here
This is very important, you need to go to the spots pictured. If you go somewhere else you will be trapped and will need to find a suicide method to get out.
Step 5: Welcome to Vice City Ghost Town
You are now free. Play normally. However, since no traffic spawns initially (just NPC's) make do with the car outside. Beats walkin, just like a 1995 Ford Escort does. Eventually, traffic will spawn. Please note some areas will be invisible so have a good memory of the city in order to navigate it, whether you're driving, flying, or using a boat. Also, all your SAVED VEHICLES in garages are able to be taken and used.
An interesting note: If you enter the door that takes you to the top of the VCN building or that of the Hyman Condo, you will spawn on top but you will still be in ghost mode
This makes it easy to find all the hidden drugs too.