There is an old school text based adventure game from the 80’s you can unlock in Call of Duty: Black Ops for the PS3, Xbox 360, and PC called Zork 1: The Great Underground Adventure.
To unlock Zork, you need to access the computer on the main menu. To access the computer, you need to mash the aim and shoot buttons (on PC, just mash the spacebar) until you break free of your restraints, getting you the Just Ask Me Nicely secret achievement (15 points) on the Xbox 360, or bronze trophy on PS3.
Once you break free, walk up to one of the computers behind you and type in ZORK to unlock the game. Playing Zork will get you the Eaten By Grue secret achievement (15 points) on the Xbox 360, or bronze trophy on PS3.
