Sandro del Prete

In this illustration, we see a window facing south in its upper part and west in its lower part. While the eyes of the viewer travel from top to bottom, the window apparently turns an angle of 90 degrees. The difference in angles is made obvious by the erroneous construction of the crossbars. But why is this window distorted? All of its lines run straight and parallel. The answer lies in the fact that the viewer is looking up at the window from the street while simultaneously looking down on it from above.