Subchamber 3 is a room in the Impact Crater in Metroid Prime. It is the third of four subchambers in the crater, and is the third area where Metroid Prime in its exoskeleton form is fought. In this room, Metroid Prime will use all four beam color attacks, in a sequence, changing after enough damage to the next color in the sequence. When damaged enough, it will fall through into Subchamber 4.
In the NTSC version of Prime, there are three tunnel grooves in the ground which allow Samus to avoid Metroid Prime when it runs across the room, but the PAL version has removed the middle groove.