Not actually my house, it was an AirBnB outside Seattle, but it's mysterious and I'm hoping someone here might know the function.
Inside the main closet in the master bedroom is a weird giant staircase leading to a square hole that looks into the area outside the bedroom. Here's the other side:
The inside of that cupboard beneath is just a small empty space, much smaller than the staircase, tiled at the bottom and possibly sized for an electric fireplace or something.
My friends and I could not figure out what it was supposed to be, and it's driving us a bit crazy.
Artefacts of a weird remodel. Owner probably on a budget or ran out of money and had to start making weird choices/compromises in order to get the thing slapped back together and shut his wife up. Lotta weird/stupid shit goes on in houses. Owners think because they understand 2 things that therefore they understand 5 things. Contractors give bad advice or propose weird solutions, often after the owner has run out of money or money's getting tight. Usually cheaper to make some slapdash mess like this than to do things correctly. As you said- it's just an air'b'nb after all. Sooner it gets rented, the sooner the cash cow starts producing milk. Most owners don't really understand the cost side of owning/building and they certainly don't understand the project management side or the time schedule side. Not a feature per-se, just some leftover evidence of either contractor or owner bungling which could have occured for any number of common reasons, almost all related to $$$$.