Call me simple and easily amused, but I never fail to be amazed by the fact that no two rings are linked to each other, yet the three as a whole are inseparable.
Wikipedia has a nice article about these rings, which are called Borromean rings.
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects