Here's a very nice item you can find in garden shops in England. It appears to be a partially-open window inset into the  wall that divides your garden into two parts. Actually it is a flat framed outdoor mirror to hang on the garden wall. Congratulations to whoever designed this!

And here is a real, unmanipulated photo of a wall consisting of small, window-like openings. If you concentrate on the light portion of each opening, you will see the wall facing to the upper right, which is presumably the way it actually faces (note the pigeons), but if you concentrate on the dark portion of each opening, the wall will snap around to face to the lower left.