Tori 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 decomposed in 4 solid tori of 6 octahedra each. These solid tori are piled up as in the picture and we have to imagine that they fold up in the fourth dimension to form a kind of ring. The colouring indicates how to attach them in the 24-cell.
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24-cell (4D geometry)