Minerals and jewels perhaps, although it has been a while. Was a hobby by me as a child to collect them. Partially motivated by the belief they would be valuable (they were not).
Greek mythology was fascinating to me as a child, although I have forgotten most of it again. Still could maybe fill an hour.
Perhaps also painting and modeling, but this would only be very shallow knowledge. There is quite a bit of formal knowledge about typography for example that really helps you design a aesthetically pleasing layout, but I didn't get to it yet.
U-boat design and their sensors. Don't know why, but I always found them fascinating. Crazy to actually use them, but fascinating. A bit of an exception because I usually find military tech to be utterly boring.
Software too of course, although I think it is a difficult topic to present. Howtos for simple electronics and in general actors/sensors would be my choice.
Aikido could certainly fill another hour. Really liked it but sadly gave it up shortly after I finished my studies. Not a good topic for a purely theoretical treatise.
Basics of sailing and different types of rigging.
And fish. Also how to cook them.