How To Unlock: Finish the 'The last hunt' mission.
“The Last Hunt” is a level that you can find in the Challenge campaign. There are limitations on gameplay in this mode: you don't have any HUD or radar, enemies do more damage, there are only a few checkpoints, no restart from checkpoint option and if you quit to main menu, you will have to restart the whole mission over. Saying all that though, its not that hard to complete. Take your time to sneak past the enemies. If you want, you can combine getting this trophy and the 10 shots trophy.
See 10 Shots for more information.