Here’s a model I designed for a recent geometric book project. It didn’t make the cut, but I thought it worth sharing. Originally made from A4, the narrowing at step 5 is partially used to replicate that geometry, so it’s not quite as pure as the original concept, but I’m happy to accept that and it folds smoothly.

The shape itself is a bisected tetrahedron, so if you make two, you can use it as a puzzle, although not a hugely difficult one!