Writing a Broadway Fantasy Novel…need help

So in the aftermath of the Tony awards as is usual with most artists, I’ve become inspired to work on something. In this case for me, I’ve been thinking about writing a fantasy novel centered around Broadway and the theatre world. I’m trying to do some research and I want to ask you all what’s one aspect of Broadway that not a lot of people know about but you do that would be perfect to incorporate into a fantasy setting…we’re talking secret societies, hidden rooms inside Broadway houses whatever it is, give me something most people don’t always know