Doors are hard flat objects a person, such as you the player, can open and close so that you can go into a room or other place. They are found all across the facility, and let you go between rooms and somesuch. There are variants of doors, the most common being a dirty, grungy, dark grey door with the SCP three-arrow logo displayed proudly in the middle on both sides, embedded into a similar grimy grey frame. The second is a giant, big filthy brownish, orange-tinted door with red stripes that is separated into two parts that, when they close, interlock, the third is the big door but compact and smaller, found all across the HCZ.
A unique variant of door not found elsewhere is found in the intro.
There is also a normal wooden door used for SCP-860 for testing.