Doors

Doors are a natural game function. The hammer comes in handy when zombies are going to the door that leads to you. They have a similar function to the window. you can also block the doors on certain maps. Mostly just Mansion.

On certain maps you need a key too open one of the doors. (I'm looking at you hospital) And zombies, how much they try, cannot open doors. So if your in a room with no windows but one door you atleast know your safe.