Catwalks are a type of obstacle or trap in Doom in which the player must navigate over a narrow bridge, usually with long pitfall drops on either side, and/or filled with a damaging liquid. Many levels in the Doom and Doom 2 feature catwalks, such as E1M1: Hangar's zigzag bridge, E1M3: Toxin Refinery's O-shaped bridge, or MAP11: Circle of Death's starting area. A catwalk can be used to make it difficult for a player to reach an item or area, as it requires the player to make very precise movements, which can be exacerbated by frequent turns, and coping with monsters simultaneously.
While catwalks can come in a variety of designs, the most dominant and manifested example of this type of obstacle appear on many parts of Doom II's MAP24. Christen Klie created a level in The Master Levels for Doom II titled "The Catwalk" where a catwalk must be quickly ran across before it crumbles to the floor to reach the exit.