IIRC The Followers of the Apocalypse area has at least 2 NPCs, one of them a talking head even, who give you hints about the Cathedral. Actually I believe the Followers' talking head, Nicole, gives you a quest to find another talking head in the cathedral, Sarah, who will give you information about what's going on inside.
That being said, the map design kind of hides the exit to the west side of Downtown Boneyard, where the Followers are, and when you get there and leave it doesn't even show up on the town map :/ So it's understandable for most people to have missed it the first time through.