Charles H. Hinton's Fourth Dimensional Cubes


"Charles H. Hinton, the author of the 1906 book The Fourth Dimension, believed he had developed a system that would allow anyone to actually visualize the fourth spatial dimension. He went one further and invented a set of colored cubes that, if used properly, would develop this 4th spatial sense."

... or drive you utterly insane. (like they did to this guy)

See also Hinton's cubes redux.