GX has an unused course named st00 in the stage folder of the ROM. It will call the assets from Sand Ocean with the track Screw Drive (Aeropolis) when unarchived or viewed through GX's model viewer debug option. Strangely, though, when using either cheat codes to access the stage in-game or using the game's debug stage viewer, it will only load universal assets such as zippers and the starting gate, along with the collision data of Twist Road (Mute City). However, it does not appear to be a test course, but it's purpose appears to be to prevent the game from crashing when starting up the stage viewer, as it always loads st00.