ペンローズの階段 彭罗斯阶梯
A famous "impossible object":[https://en.wikipedia.org/wiki/Impossible_object] created by Lionel & Roger Penrose. A [[stairs|staircase]] which one can continually ascend or descend yet return to one's starting point. Sometimes called an [[optical illusion]] for convenience sake.

h4. External links

* "Wikipedia: Penrose stairs":https://en.wikipedia.org/wiki/Penrose_stairs
penrose stairs