In the prologue to the game (in Dubai), fairly early on you will come to a door with a keypad which you have to go through to continue (you need to restore power to this door as part of the main quest). If you enter the code "0451" it will unlock the door and award you the achievement.
You could get through the door without the code (e.g., by hacking it). The code itself is an Easter Egg from the game series, but is also found on a construction plan you will pass shortly before encountering the door.