Horizontal Door Example is a Single Player level. There is no in-game name for this level, nor is there any name included with the documentation. The level name instead comes from commented lines inside the .map file.
This level features a single Movable Wall that is treated as a Door. When the player moves towards the Moveable Wall, it opens at a slow rate and moves to the right. If the player leaves the immediate proximity, the Moveable Wall will close after two seconds.
This level is relatively similar to Vertical Door Example, though the Movable Wall moves to the right instead of upwards.