Board Thread:Manga/@comment-43435318-20190808223013/@comment-36306777-20190809142540

That's such a common shape. Those are just the two arches of a type of window called bifora (see pic). Also do you mean you can see the upper window as a window, but not the lower one? It's got the same features, they're just less exposed due to the shape of the frame.

(I'm not saying thie bifora in this picture has exactly the same structure as the one drawn, but the shape of the two inner arches may vary a lot from case to case, and it can very well resemble a human shape from afar)