Wikipedia:POTD column/October 23, 2006

In this example of isometric projection, the blue sphere is two levels above the red one, but this can't be seen locally. If the pier that the blue sphere is on were extended by one square, it would align perfectly with the square the red sphere is on, creating an optical illusion. Some of the famous "impossible architecture" works of M.C. Escher exploit this isometric limitation.

Illustration credit: Algr/Icey
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