What is impossible geometry?

One innovative area of recreational geometry that has rich potential to engage and challenge a wide variety of students is “impossible geometry.” An impossible geometric object is a two-dimensional drawing that gives the impression of a viable three- dimensional figure, which in fact cannot exist.

What are all the impossible shapes?

Four of the most well-known impossible shapes are the Penrose triangle, Penrose stairway, Freemish crate and the impossible trident [source: The Worlds of David Darling]. The Penrose triangle, aka the tribar, is named after physicist Roger Penrose.