An ancient language like Greek or Latin
A trade/ handiman skills
How to artistically plate food
About the work of Ray Peat (h/t nostr:nprofile1qqsr26r4lltjnvrwadxp67ns58m4qpzaqemhf5sup7hlujhjh7t296qprpmhxue69uhhqun9d45h2mfwwpexjmtpdshxuet5qy8hwumn8ghj7mn09eehgu3wvdeqzrnhwden5te0dehhxtnvdakz77f8s05)
Understanding your local civics
History of architecture
How to improve privacy
You can also zero in on some character flaws and figure out how to improve upon them.