The oct-tet truss (more properly called a space-frame) is a structure built of octahedral and tetrahedral elements. Together, octahedra and tetrahedra can tesselate 3-dimensional space.
The images on this page show that octahedra and tetrahedra can themselves be constructed out of octahedra and tetrahedra. This idea can be applied recursively to produce a fractal oct-tet truss.
To give a sense of the scale of the models, this is me next to one of them.
