3D printed rendition of Penrose's impossible triangle
This 3D printed rendition of Penrose's (sometimes referred to Escher's) impossible triangle makes a great conversation piece.

Printed in Green PLA, this print took 16 hours to complete. Often depicted in 2 dimensions in print, it’s an optical illusion example of a triangle which seems impossible to create in 3D.
This illusion has been around since 1934 when Swedish artist Oscar Reutersvärd first created it.