Escher´s waterfall. Real or not?
Escher´s waterfall depicts a seeming paradox where water from the base of a waterfall seems to run uphill prior to hitting the top of the waterfall.
Although most 2D artists use relative symmetries to create an illusion of depth, Escher exercises contradictory symmetries to create the visual paradox. Waterfall has the structure of a Penrose triangle, an unacceptable object planned independently by Roger Penrose and Oscar Reutersvärd.