The Café Wall Illusion is an optical illusion that was first discovered in the late 19th century. It is an example of an ambiguous figure, where the same image can be interpreted in multiple ways. The illusion is created by a grid of alternating black and white tiles, with slight variations in the
From Wikipedia
The café wall illusion is a geometrical-optical illusion in which the parallel straight dividing lines between staggered rows with alternating dark and light rectangles appear to be sloped, not parallel as they really are.