Oh, let’s say . . . the history of buttons. Or how to make color prints. The technology of katana. Diamond cutting. Wedding customs of Peru. Food coloring. Digestive system of the snail. I could go on.
Ancient shipbuilding. It’s incredible how they managed to build advanced engineering projects with basic tools and no formal system for calculating loads and forces etc. Oh and it’s watertight, life/death if it fails and gets violently pushed around by waves most of it’s existence in a highly corrosive marine environment. It would be interesting to learn more about how the hell they figured all of that out and write up a report.
Oh boy. Quite a bit. There’s so much I don’t know. Mathematics for sure. Chemistry. Other languages. Even stuff I’m familiar with I’d want to research first.