Rhombic Dodecahedron Mirror Box
The rhombic dodecahedron is a twelve-sided solid. Each of its sides are identical equilateral diamond shapes (rhombs). The ratio of the diagonals of the sides are 1/√2. The sides are in the angle (dihedral angle) 120°. Consequently it has many unique properties. One is that copies of it can be arranged face to face to fill space without any gaps. Importantly, it is one of a few geometric solids, like the cube, that are also space fillers.