Item description:

All you need to do is find the last Artifact which is in the Bank vault it is on the floor but after you pick it up a Librarian will confront you all you have to do is stand still and aim in but do not fire and he will sit there and do a little thing and then just walk away, when he does just crouch walk to the exit which will be directly in front of you when you exit the vault.

To get into the vault take the sewer tunnel to the left when you exit the Ranger Outpost, and then take ladder upstairs to the surface and then there should be a red door as you climb up go into the red door and you will see a hallway and another red door go to that and follow it down to the vault.

The last artifact is the Secret Subway Map all you need to do is grab it and it will unlock the achievement! :)