02-10-2019, 10:16 PM
I wonder if "gallery" would actually still work. Technically it's still a covered passage that is open at one side. You could even just write it out as "the second floor opened into a rectangular gallery in the center." Since gallery carries connotations of viewing or looking down from above. It's also possible that if you dig up the proper architectural term for it no one other than architects will understand it.
https://www.britannica.com/technology/gallery
If you search for images of "second floor gallery" you'll find a few that look like what you're describing.
https://www.britannica.com/technology/gallery
If you search for images of "second floor gallery" you'll find a few that look like what you're describing.