Here's what the Swedish artist Oscar Reutersvard did. In 1934, he got himself a pen and paper and drew four cubes, like this. He called this final version "Impossible Triangle of Opus 1 No. 293aa." I ...

In an impossible figure, seemingly real objects—or parts of objects—form geometric relations that physically cannot happen. Dutch artist M. C. Escher, for instance, depicted reversible staircases and ...