0x0x0 Rubik's cube is a non-twistable non-existent cube. However, it does exist as a concept.
This cube has no dimensions because it has no spacial geometry. It is like a point in mathematics as a zero-dimensional object.
Many cubers will say that this is a most difficult puzzle to solve and even more difficult than the 1x1x1 Cube but usually, these are just the inside jokes of the cubing community. People from the outside of the community may get a bit confused thou and that's the joke part.