I recommend Kokchi Sugihara's website. https://www.isc.meiji.ac.jp/~kokichis/Welcomee.html https://www.isc.meiji.ac.jp/~kokichis/Welcomee.html There's a prin

I recommend Kokchi Sugihara's website. https://www.isc.meiji.ac.jp/~kokichis/Welcomee.html https://www.isc.meiji.ac.jp/~kokichis/Welcomee.html There's a printable gravity hill sculpture among other optical illusions. His back story is that he was working on machine vision for taking in 2d scans of technical drawings and reconstructing the 3d wire frame. Just for the sake of experiment, he fed the program an impossible object and was surprised to find it output some coherent 3d shape. So naturally he built the shape and sure enough, from a specific angle with one eye closed, it looked like the original impossible construction. He's been making impossible constructions ever since.