Robin Hood - Sherwood Builders

You get this for completing Little John’s side quest “merry men’s operations”near the beginning of the game after completing tutorial. Talk to john to a tree as marked on map where you’ll be introduced to stealth and backstab. Proceed to the bandit camp marked on map. There will be an archer and second bandit walking around, so take them out. Walk a bit further into the camp and you’ll see a third one or acting against a skeleton. I was able to backstab him easily by crouching with B and approaching with RT when close behind. He will drop a door key that you use on the tree door as marked on map. Take everything from the treasure chest inside then return to John and talk with him to get this achievement.