: Go to your game installation directory (usually Steam\steamapps\common\Call of Duty Modern Warfare 3\players ).

Before you delve into editing game files, it's worth checking one in-game setting first. While the option alone may not always be sufficient, it's the official starting point.

seta developer "1" seta sv_cheats "1" (Single-player only)

: Press the tilde/grave key again to close the console and return to the game.

Press Alt + Tab to return to your desktop and launch .

Alternative Environments: Dedicated Servers & Third-Party Clients

– Allows you to fly through walls and explore outside the map boundaries.