"Impossible" objects are those that are impossible in three dimensions, but can be created in two dimensions to make an illusion in three dimensions. The cube displayed on the stamp below is used by M. C. Escher in both Man with Cuboid and Belvedere, from 1958. In Belvedere the structure also is based on the impossible cube. Waterfall, 1961, also explores the cube.

     The three stamps from Sweden show work by Oscar Reutervärd, a Swedish artist. In 1934 he drew the first impossible triangle, using nine cubes. This figure, is titled Opus 1.

Opus 1