Hints for the cursed letters?

[Chorizo Joe]

I'm stuck looking for the 4th location and I'd love some help please.

In case you need help with the others here's what I found:
1st is the the huge mirror in Two moons. The mirror is located near the mirror side of the boss room. Just kneel in front of the mirror for a few seconds
2nd is the pit near the confession place .
3rd is in Mother of Mothers. Look for a broken bell (the same kind that one enemies uses to charge at you) and attack the wall.
I'll make a guide once I'm done (if no one else does)

[hauntergeist]

Thanks for the hints. I didn't figure it out and looked up the last letter location. It's so obvious when you know it and it's perplexing why the event is not triggered accidentally! Hint: Check the City of the Blessed Name. It's there but visually not so easy to spot.