I was in the shower yesterday and said "Oh no, a loose tile!". 5 hours after the shower, I'm here, as the tile was not just "loose" but water had gotten all into the wall and was wet. So at this point I've torn out all the wet parts, but to my surprise, there's an airduct hidden behind the wall, going nowhere (red arrow):
I stuck a towel into it so debris wouldn't fall in, but here's how it looked after I pulled the drywall off, completely open:
No way this is supposed to be like this, right? Tell me this was a screwup by the builder and they forgot to close it off?
The furnace is right below the bathroom, and a very short run duct is going to this location. On the opposite side of this wall is the closet... I always wondered why it was so warm in there.
What should be done about this? I could easily remove the ducting from the furnace and seal up the hole if that's the job required.

