Parallel Towers of Pisa

You’re looking at the winner of the 3rd Annual Best Visual Illusion of the Year Contest. I admire it for its simplicity. As the web page describing the illusion explains: “Normally, if two adjacent towers rise at the same angle, their image outlines converge as they recede from view due to perspective, and this is taken into account by the visual system. So when confronted with two towers whose corresponding outlines are parallel, the visual system assumes they must be diverging as they rise from view, and this is what we see.”