Turok

All you need to do for this achievement is to kill one hundred soldiers stealthily with the knife. A good place for this is the chapter "Bad Blood", simply progress through the level as normal until you reach the part outside with the pipes, you get told to be stealthy in this area so do so and you will be able to get up to eight kills per trip. Once you run out of enemies to kill, save your game and repeat this process until the achievement unlocks.