Located in Ganton, Los Santos, the gym becomes accessible following the mission Drive-Thru. Carl Johnson can learn boxing moves at the gym, as well as use the other facilities to increase or decrease certain statistics, specifically stamina, muscle and fat.
One common use for the gym is the hole in the roof which allows access to Hidden Interiors Universe, which requires the player kill everyone inside, using the jetpack cheat code to acquire a jetpack, and walking towards the door with the jetpack, lifting the player off into the Universe. Using this the player can enter several non-used interiors, you can even enter Liberty City, which is a left over object from the mission Saint Mark's Bistro.
- In a beta screenshot, the boxer that you can challenge had a much different appearance, wearing long pants and a bandana. He also just stood upright instead of punching the bag.
- In the same beta screenshot, you can see that the yellow posters around the room aren't there and there is a pedestrian walking around. This suggests there were going to be ordinary people in there as well as the boxers and the cheerer.
- Park a car with its front end touching the front door of the gym, and then walk into the marker to enter the gym. Then, when you are inside, exit the gym, and you will spawn inside a small room behind the front door of the gym, which is normally inaccessible to the player. The walls aren't solid, and if you walk through them, you will fall into Blue Hell, and then spawn outside of the gym on the sidewalk.