600-cell
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In geometry, the 600-cell is the convex regular 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol {3,3,5}.
It is also known as the C600, hexacosichoron and hexacosihedroid.
It is also called a tetraplex (abbreviated from "tetrahedral complex") and a polytetrahedron, being bounded by tetrahedral cells.
100 tetrahedra in a 10×10 array forming a Clifford torus boundary in the 600 cell. Its opposite edges are identified, forming a duocylinder.
Platonic solid
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In geometry, a Platonic solid is a convex, regular polyhedron in three-dimensional Euclidean space. Being a regular polyhedron means that the faces are congruent regular polygons, and the same number of faces meet at each vertex. There are only five such polyhedra:
Kepler's Platonic solid model of the Solar System from Mysterium Cosmographicum (1596)
Icosahedron as a part of Spinoza monument in Amsterdam
A set of polyhedral dice.
Image: Kepler Hexahedron Earth