Origins.

Buried.

Green Run.

Nuketown Zombies.

1

Press Start on the main screen when you first start up the game. ...

2

Tap the L2 and R2 buttons on the PS3 (or LT and RT on the Xbox 360) rapidly and repeatedly to stand up. ...

3

Walk forward and turn to the left.

4

Move along the wall until you arrive at a computer.