Structure Illusion
Optical illusion of a structure impossible to figure out.

Optical illusions happen when the brain perceives the image of an object in a completely different way than the actual object is. An impossible object is also known as impossible figure or un-decidable figure. Such image is a type of optical illusion that consists of 2 dimensions and gets instantly and subconsciously interpreted by the visual system as a three-dimensional object though it is never geometrically possible to have an existence of such an object. In most of the impossible object illusion, the impossibility becomes visible when the image is looked at for some seconds. Initially the brain gets the impression of the 3D image that remains there even if it is contradicting. In some of the examples of impossible objects the impossibility does not seem spontaneous and the viewers have to consciously examine the geometry of the implied object to understand that it is absolutely impossible. For ages, impossible objects have been a topic of immense interest among the artists, mathematicians and psychologists. Some of the important impossible objects are impossible cube, penrose stairs, penrose triabgle, bilvet( or devil’s turning fork). British psychiatrist Lionel Penrose and his son, Roger Penrose, a mathematician submitted an article to the British journal of Psychology with the title “Impossible object”. The examples of Penrose triangle and penroe stairs have been given there. The Dutch artist M.C. Escher had drawn many drawings with paradoxical effect. In 1957, the first drawing of Escher was produced which had a true impossible object- cube with magic ribbons.
Optical illusion of two men walking on the impossible way.

Source: “Walk infinity” by Ricardo Baigorria