Rubik's Cube - Variations Upon

There is an enduring fascination with Rubik's cube. Invented by Ernő Rubik in 1974, I first saw it in Macy's department store in New York in 1980 when its popularity was beginning to take off. It is still popular over thirty years later.
As if it wasn't seemingly hard enough already, versions with different shapes within the cube format have been appearing in recent years. I say 'seemingly hard enough'; it has now been established that any combination of the cube's facets can be solved in 20 turns or fewer.