13 Faced, Space-Filling Polyhedron

"A space-filling polyhedron, sometimes called a plesiohedron, is a polyhedron which can be used to generate a tessellation of space."

What that basically means is that these two polyhedrons, when paired together, can create an infinite pattern of identical polyhedron pairs that fully fills space, leaving no gaps in-between.

You can learn more about this specific polyhedron from the link:
http://science.unitn.it/~gabbrielli/p8_gallery.html