What is this hatch-window thing in my 1911 house is called? : architecture

Hello architects! I just recently moved into an old house in Vancouver, Canada and have a very interesting feature attached to my bedroom; it’s a separate room with a kind of port-hole that swings open, making the room into a balcony (?) (refer to image). The room itself is covered with siding that you would see on the outside of a house, white the “door” that swings open is made of thin wood. The house was built in 1911 but hasn’t been particularly well preserved/maintained, so this might be a newer addition (?) but the hardware looks pretty old to me. It’s all attached to my bedroom on the second floor of the house.

I was hoping somebody could tell me what this window/door thing is called, and what the room is meant to be used for! Right now I’ve set up a little art studio/office space but I’m really curious to learn more, as my google searches have been unsuccessful.