The famous twelve-sided platonic solid, created in FreeCAD.

A platonic solid is a body where all the faces are identical in shape and size, with identical edges and angles, and the same number of faces meet at each vertex. There are only 5 platonic solids in 3 dimensional space:

1. Tetrahedron (4 faces)
2. Cube (6 faces)
3. Octahedron (8 faces)
4. Dodecahedron (12 faces)
5. Icosahedron (20 faces)

The dodecahedron is one of three platonic solids with triangular faces. Platonic solid shapes are often used for dice due to their symmetry and regularity, giving each face an equal chance of landing facing upwards when rolled.

Credit to Ray Fox for being the first to upload a public domain dodecahedron mesh. Also, check out Steve DeGroof's customizable D12 model.