Impossible tribar

This model is also called the 'Penrose Triangle'. The configuration is impossible to create in 3D, using full cubes (with all 6 sides intact for each cube). What you are looking at is an optical illusion, where only 3 adjacent-to-each-other walls from each cube are included, and the inside concave corners masquerade as external convex ones :)

Also, I used this model for the cover image of my 2004 book, 'Rendering for Beginners': https://smartcg.com/tech/cg/books/RfB/home/index.html

The book cover is mentioned in this article, which also has more info+links regarding the tribar model: https://mathworld.wolfram.com/PenroseTriangle.html

And, here are my alternate versions of the tribar: https://www.shapeways.com/model/672155/penrose-tribar-with-stand.html and https://www.shapeways.com/model/670170/impossible-tribar.html.