When an artist renders three-dimensional objects in two dimensions, they normally give it perspective, so that it appears realistic to the eye. However, since the two-dimensional medium (a computer screen or a canvas) has no depth, you can mess around with the perspective part and really have fun. M.C. Escher was a master at such shenanigans. His use of confusing perspective inspired Macedonian artist Fleta Selmani to create the font she calls Impossible Type. Letters are three-dimensional, but their perspective defies reality.
The font is not difficult to read, as our brains perceive basic shapes in total at the speed we read, but if you stop and look closely at the letters, they are mind-bending. You can purchase and download Impossible Type (upper case, numbers, and punctuation) here.