3D TESSELLATIONS 1:
This paper or cardboard 20-sided 3D tessellation by Seth Bareiss
is easy to make, and an ideal 3D geometry project for art or geometry class. It folds up neatly into a "platonic solid" made of 20 triangles. That kind of platonic solid is called an icosahedron.
To make it, you'll need scissors, glue, a printer, and paper. Just print two copies of the picture at right, cut along the outline, and start folding.
Hint: After cutting out each star shape, fold each paper into ten equilateral triangles; then fit the two pages together, and finally glue or tape them permanently.