At the side of the Prawn Island bridge going to Vice City Mainland. Run onto the wall until you fall in Blue Hell, and you will respawn at Diaz's mansion.
The player can also enter Blue Hell by running towards a corner and getting hit by a tank. This with cause the player to fall into Blue Hell and spawn at the nearest land 10 to 15 seconds later.
Use a vehicle and go to an invisible wall near the freighter in Viceport. Drive and bail out and swim at the invisible wall until you have entered the wall. Swim until you see a hole, then enter the hole. You will fall into Blue Hell and reappear on the nearest piece of land.
Fly a Skimmer to the Prawn Island bridge (either InterGlobal Films or one of the mansions). Exit the Skimmer and walk until you are swimming. In the InterGlobal Films loop, swim all the way. If you use the mansion, this is dangerous. It will be split into phases. Try to swim carefully as you can suddenly reappear into the surface, you will go down and swim more. The end of the route is at the road lanes between the three mansions and InterGlobal Films road, then you will fall and spawn later. If you fall on the box, you will spawn in the Mendez Mansion. Note:The place is at Downtown-Prawn Island bridge.