This lesson is a prelude to a look at the fourth dimension. It is a consideration of the third dimension by 2-dimensional beings, similar to the book Flatland by Edwin A. Abbott. M. C. Escher and his works are also discussed. 3-dimensional polyhedron such as a tetrahedron, cube, octahedron, icosahedron, and dodecahedron are analyzed as they pass through a 2-dimensional plane. Also shown are stereographic projections of the polyhedron on a 2-dimensional plane, and they are identified by their projections.