If you go forward in the bell tower, after a short time you come to a ladder that is hanging high up and which you can then lower down from above. After almost 300 hours in the game and 1 year after the release, I have finally solved this mystery for myself. You only get to this point later on and to do so you have to defeat the "Receiver of Sacred Resonance" as a Boss. Only then do you get to this point and admittedly, it is almost pointless to extend this ladder. Because you don't actually have to go to this point again.