Was teaching third angle projection and a student managed to produce an Escher version of it unintentionally. Took us a while to figure out where he went wrong. I kept that drawing for years, had a change of staffrooms and didnt notice it go missing.
From the Brilliant Mind of M.C. Escher - Dutch Artist (1898 -1972)
If this doesn't mess up your mind, I don't know what will !!!
1. The rod in the middle does not exist.

2. How many, 7 or 10. Count at the top and then at the bottom..
3. Is the door open to inside or outside?
4. Round or square?
5. How many, 3 or 4?
6. Is this just one?
7 Rare construction.
8. The center beam disappears, look from left to right.
9. 2 or 3?
Clever!
