Trap

Traps vary in definition. They can refer to mere environmental hazards that the player must navigate, or they can be more intricate. Many Doom levels have booby-traps for example, that release a squad of monsters on the unsuspecting player when they throw an innocent-looking switch. Some traps are baited with a big gun or powerup, and are activated when the player walks up to the item to grab it. Almost any kind of trap is considered fair to a degree as long as it is beatable, and can add a much needed element of surprise to an otherwise mundane level.

The first trivial example of a trap appears on E1M1: Hangar, where the player must navigate over a zigzag bridge over a pool of nukage.