I can barely see what it is you are asking about.

Hmmm...it's a strange bump out on the wall near the ceiling. It's the only pic I have.

Open it up and see what is in there there is no way for us to know,

I circled it. I can see it, but, of course, I know what I'm looking for. Can you see the entirety of the photo?

Thanks for checking it out, anyway!

It's coming up as a really tiny photo, but we can't tell unless you cut into it anyway. Sometimes in old houses when there's something immovable, they will just box it in with drywall as opposed to framing the whole room around it and making it much smaller. It may be a brick chimney that had to take a jog or some other kind of ductwork.

I can see it the bump out, but don't know the anwser. sorry.

Thank you! I was also think chimney related.

What is on the other side of that wall?

It's an exterior wall.

Anything coming out of the roof at this spot, like a gas flue or plumbing vent?

It's likely a bumpout for a duct that couldn't be buried in the wall. If you go outside and look at the roof above that area, you may even see a roof vent.

Is there attic space above it? Maybe you could check there

Thank everyone. I’m not currently in town, but I will definitely check the roof above this for clues.