In geometry, the grand 120-cell or grand polydodecahedron is a regular star 4-polytope with Schläfli symbol {5,3,5/2}.
It is one of 10 regular Schläfli-Hess polytopes.
It is one of four regular star 4-polytopes discovered by Ludwig Schläfli.
It is named by John Horton Conway, extending the naming system by Arthur Cayley for the Kepler-Poinsot solids.
It could be seen as another 4D analogue of the three-dimensional great dodecahedron due to being a pentagonal polytope with enlarged facets.