My brain can't right now
Mobius Cube With A Single Side Milled From A Solid Block Of Steel

This is a video of Youtuber Inheritance Machining creating a Mobius cube — a cube that, like it’s Mobius strip cousin, only has a single side. My brain hurts just thinking about it. I remember the first time I saw M.C. Esher’s Mobius Strip II (with the red ants) I assumed it had to be one of his perspective tricks. This cube? I started following one side all the way around, and I have to admit, I got lost almost immediately like in the funhouse at the fair. “We found him crying on the floor in a mirror room after an hour.” Honey! “What?” I was so ugly.

Keep going for the video, and he runs the entire side with a Sharpie at 24:25.