Beekeeping. It's fun to do and can produce a lot of high quality products. This leads to learning about the different things you can make with honey (creamed honey, mead, candy, etc). What to do with wax (candle making, cosmetics, wood finish, etc). Learning about how the hive behaves and such is very interesting. It also makes you pay attention for flowers too (look up honeybee and skunk cabbage for an interesting thing you would learn if you saw bees bringing in pollen during very early spring when it looks like nothing is blooming).
Mycology is another interesting one. You can forage and cultivate Mushrooms. You find a lot of cool fungi while foraging, some of them edible. But you notice a lot of stuff that maybe you wouldn't have noticed in nature before. You often need to learn to identify trees too. On the cultivation side you lean about sterile techniques and building a home lab. Of course either path can lead you to new cooking ideas (lions mane "crab" cakes anyone?), and some very cool facts about fungi in general.
Track days and autoX are fun. Not only is there a ton to learn about driving techniques but also a lot about engineering and mechanic work when doing maintenance or upgrades. Even researching stuff that's not available to you right now can be cool, like the tech used in F1 that might become commercial in another decade (or not).
My list is extremely long. But those are a few.