Penrose stairs: four flights that endlessly climb in a loop. The illusion only holds near the default view, so camera rotation is intentionally limited. M.C. Escher's 1960 lithograph "Ascending and Descending" popularized this impossible object, based on the 1958 Penrose stairs devised by Lionel and Roger Penrose. In reality each flight rises about 3.4 units, so four flights would net a real height gain, but the forced-perspective loop tricks the eye into perceiving continuous ascent with zero net elevation change. Five colored figures endlessly climb the loop, each offset in phase so the procession never ends. Zoom and pan freely to inspect the stonework.