A torus in the 24-cell
The 24-cell (that is one of the six regular polytopes in dimension 4) is made of 24 octahedra and can be split into 4 solid tori, each composed of six regular octahedra, piled up as in the photo. You can try and imagine them to fold up to form a ring in the fourth dimension. The colours indicate the way in which the 4 tori must be attached in the 24-cell.
© matematita
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24-cell (4D geometry)