I’m a huge History nerd. Just went back and got a History degree just for fun and got paid to do it (Post 9-11 GI bill). I don’t particularly care for History books, but generally love History podcasts. In the past few years I’ve finished a 200+ episode podcasts on the History of Rome, World War 1, The Russian Revolutions, and World War 2. Some anecdotes in those are things I’d never heard of, like a German submarine popping up in Baltimore Harbor in 1916 before the USA joined WW1, unloading tons of industrial dyes in exchange for tons of rubber, nickel, and other strategically short war materials. Learning History is world building to me. The more I learn, the more the pieces fit together. My son (10) is getting into it and I really enjoy teaching him about the subject.
I’m an education nerd in general, that History degree was my fourth, all of them paid for by scholarships and/or employers (except the first, thanks Mom and Dad). I am also big into certifications for work holding over a dozen big IT certs (PMP, CISSP, CCSP, CISM, etc.). These are all paid for by work and I am one of those crazy people that enjoy working on these. Working on CYSA+ now.
I am a big fish nerd. I’ve only got a 50 gallon saltwater tank right now, but it is established enough that I am taking coral out of it to sell/trade on a weekly basis now. Big upfront expense, but more than paying for itself now.
I am also really big into science fiction and fantasy. I am a few months away from watching every episode of every series of Star Trek with my wife (life goals). I have been pouring hours into reading Sanderson, Jordan, Corey, and have a lifetime more to read.
There are not enough hours in the day for all my fun hobbies.
Also… pinball and multicades. Big upfront expense, but I’m way “up” on paper, so how much does it cost really?