At Burgundy, France, you go into the house (not broken) and go to the room with the turret.
Jump onto the window with the turret and turn left (you should be facing a tank).
Walk very slowly off of the window facing left, and you should fall onto an invisible ledge.
You can go all the way around to the chimney, but you should crouch to move easier.
This glitch is not patched, and can still be done, if you need help send me a message TC257.