Having created the illusion of an expansive corner window using smoke-and-mirrors in our Harlem space (below), we LOVE seeing other riffs on the theme of optical illusion windows. Granit Chartered Architects devised a brilliant faux bay window by building bookshelves on either side of an ordinary window, then buildt a window seat between them. They installed mirrors on the two vertical sides of the bookshelves and finished the whole thing with molding to look built-in Brilliant!
This kind of optical illusion will only work if you have a wall that connects directly to the corner/edge of the window as was the case in our cheap construction building.
Otherwise, there’s always this interesting illusion with a mirror ABOVE the window, at just the right angle to show the view.