I live in a house that features: a legit secret door in the back of a closet, a small nailed shut door in the back of another closet, a hallway that goes nowhere and dead ends in a painted window with six latches on it, and a pantry under the stairs with shelving that would confuse M. C. Escher.
So, that should contextualize things when I tell you that my "office" is a 10x10 cell that is ever so slightly narrower and shorter in the back than in the front, and features an irregularly shaped niche on one wall that I just call, "the confessional."
I really couldn't make this house up if I tried.
I'd make sure there's not some secret eldritch ritual room behind that nailed-shut door.
With that said, there's kind of a catch-22 there; you want to know if there's stuff going on behind it, but you also don't want to stumble into Lovecraftian horrors.
Pics or it didn't happen! Seriously tho, that sounds like an awesome location for a modern-ish horror game! I may have to use this!