In Esplanade North, San Fierro, the player will see several docks jutting out into the San Fierro Bay with warehouses situated upon them. Next to one of these docks is a submarine called the USS Numnutz. If the player swims directly down from the submarine to the bottom of the waterway next to the dock, they will notice a greyish color which does not match the color or texture of the surrounding rock. This area is actually a hole that the player can swim through to enter Blue Hell.
If the player stands on top of a San Fierro tram and takes a picture with the camera while on the tram, CJ may fall into Blue Hell and after a few seconds, and eventually land on the sidewalk.
Also in San Fierro, there is a large clothing store in Doherty, opposite the tract of wasteland. The top portion of the wall (between the top floor and roof) is not solid and can be accessed with a jetpack.
In Mulholland, Los Santos, there is a newspaper shop with a non-solid area under the roof's overhang which will lead to the interior of the building, and from there to Blue Hell itself.
Get a jetpack, then go to the Mulholland Safehouse. The inside corner of the house is not solid. Walking through it will make you fall underneath Los Santos. You can use the Jetpack to explore the city via the "underground". Otherwise, if you walk through the unsolid wall without a Jetpack, you'll fall for a while and re-spawn in the street.
At Las Venturas Airport, one of the walls of the main building has a glitch wherein running at it enough will pop the player through into Blue Hell. The wall is located where the fence around the runway meets the building.
Also in Las Venturas, there is an unmarked Pay 'n' Spray east of the casino in the Come-A-Lot district. The southwest corner of the Pay 'n' Spray is not solid; if the player enters that spot via Jetpack and lets Carl Johnson sink into the hole for a while, he will fall into Blue Hell, later automatically spawning on the sidewalk outside the Pay 'n' Spray.
Outside the Ammu-Nation in Red County, enter the Jetpack cheat (or use your own) and walk in front of the entrance. The yellow marker will disappear. When this happens, lift up and you will fly into Blue Hell.
Before End of the Line, you can blow up the big wall with explosives and inside will be Blue Hell.
If you go far out enough into the ocean and swim to the bottom of it (you must have full health/lung capacity so you live long enough) the ocean floor is not solid, and you will respawn somewhere in San Andreas. If you die in the process, you will spawn dead somewhere in San Andreas on the sidewalk.
There is a building in Juniper Hill, San Fierro, in which one spot on a wall is not solid, but can only be accessed with a Jetpack. It leads to the interior of the building, and then to Blue Hell. The building is between a clothing store and a safe house.
Also in Dillimore, Red County, there is a Discount Furniture store. Its name is not shown in the shop, but it is a building with a lot of signs and stickers on the windows. It's not an enterable building, so there will be no yellow marker at the entrance, but go to the entrance with a Jetpack, and fly up, and the roof will not be solid.
If you spawn a vehicle with the driver's door in a wall (so that the vehicle is partially immersed in it), get in it, and then exit it, CJ may exit on the driver's side. Since the door was inside the wall, CJ will now be inside of it as well and will fall to Blue Hell before re-spawning on the nearest street.
In Tierra Robada, below the Robada Intersection and between the Garver Bridge and the Kincaid Bridge, there is a section of unsolid terrain along the small cliffside above the sea. Obtain a Jetpack and fly downwards against the section for a while, and pretty soon, CJ will be popped into Blue Hell.
There is a tall rock somewhere in the roads of Flint County. You will need a fast vehicle to enter blue hell via the rock. Make sure you drive very fast, or it will not work. If it works, you will fall down into Blue Hell and re-spawn in Back o Beyond. If you try this again, you will respawn somewhere in Flint County near Los Santos.
In Temple, Los Santos, in front of a tall building, climb your vehicle to the stairs, turn left and drive to a right-most part of the wall. This can only be accessed by small vehicles.
Sometimes the game will poorly render and you will be able to see Blue Hell under the solidity.