Everyone's a nerd about something. What are you a nerd about?

I know it's an unpopular opinion given current circumstances, but I've always been a huge nerd about Russia. The history, the geography, the music, etc. And as an American, I've always found it fascinating how U.S.-Russian relations have fluctuated over time. We've gone from allies, to enemies, to frenemies. This doesn't mean I support Z or Putin, of course. What are you a nerd about?