Borremean Rings (Q68406)

Technically not rings, these ellipses are topologically equivalent. Suggested by a colleague (thanks Dirk), these show off the power of 3d printing. In case, you aren't familiar with these, none of the rings are actually linked with the others, yet they cannot be pulled apart (without breaking them). The only other way of creating them without joins is to carve them from a single peice of material.