Penumbra: Black Plague (PC)
Complete the game with all ten secret artifacts collected to get the password "xor451". Run the "super_secret.exe" file in the game's installation directory and enter xor451 for the password when prompted to view concept art, desktop backgrounds, and a video.
Space shooter mini-game
During game play, access Swanson's computer and run the program "schmup.exe". Enter xor451 as a password to play a space shooter mini-game.
Hiding from the zombie
Put a lot of objects over each other and create a "wall". The zombie will not be able to find you.
Put objects in the door (for example, boxes). The zombie will not be able to go through. Wait a short time and it should leave.
Strategy guides from GameFAQs