One Montessori exercise for veery young children consists in providing them two boxes and a number of geometrical solids made of wood, with instructions to put together in one box those forms that are angular, like the tetrahedron and the cube, and in the other those that are smooth to the touch, like the egg and the sphere.
Projective Ornament by Claude Bragdon, 1915.
Prince Rupert of the Rhine won a wager that a hole could be made in one of two equal cubes large enough for the other cube to slide through.
The Math Book by Clifford A. Pickover, 2009.