The building appears during the Big Smoke mission Just Business. Although little is known about the interior, it has several stories and has a statue depicting a man touching himself inappropriately. Some statues facing the one touching himself have their hands over their eyes. There is a body armor in this building and several unusable lifts.
- Leaving the building through one of the doors (only one works) then entering it backwards with a pistol aimed forwards will enable the player to "ghost" through the door and into the actual interior, rather than the separate one. The floor here is, aside from a small square by the door, not solid, and the player can fall through it, entering Blue Hell.
- Similarly, if the player enters the building and then leaves doing the same thing, they will go back outside to Los Santos, however the game will detect that the player is still inside, and thus, no vehicles will be loaded and the entire San Andreas apart from the area immediately surrounding the building will become invisible (although still solid). All pickups, collectibles etc. will still be there and, by going back into the Atrium and out again, or any other interior for that matter, the glitch will be eliminated.
- When the player enters through the northern door, the in-game text says that the building is called the Atrium. When they enter from the west, it says Attrium, which likely is a text error.
- The Atrium is a part of the heart where blood flows through.
- If the player leaves a vehicle outside the front of the Atrium, at least in front of the 2 escalators, and the player enters then exits the interior of the Atrium using the glitch mentioned above, then the vehicle will be outside in the place the player left it. It is enterable and controllable, but it is invisible. However, navigation through the city is difficult, as the whole state is invisible, as is the car.