Mr Green61,832 31 Oct 2021 13 Nov 2021 13 Nov 2021
When you have collected all the items and pulled the lever in chapter 1, go to the room where the deceased Boris is in and walk up to the poster "Bendy In Sheep Songs" (which has Boris holding an instrument). You should be able to walk through that wall.
Notice: You are unable to get this achievement before getting all the items and pulling the lever.