Dutch crack the origin of Escher’s impossible stairsmain
M. C. Escher said in 1963: ‘I cannot help mocking all our unwavering certainties. It is, for example, great fun deliberately to confuse two and three dimensions, the plane and space, or to poke fun at gravity. Are you sure that a floor cannot also be a ceiling? Are you absolutely certain that you go up when you walk up a staircase?’
Solution here (in English).