Metal guitar, comic books, epistemologies. A lot of people write off metal as just distortion and shouting but it's a huge genre like jazz or classical without as long a history. Comics interest I stopped for awhile but got back into it and helped me learn drawing and story writing to better appreciate the artistry. Epistemologies from an interest in reading philosophy books and that was just the subtopic that always held my interest most.
And not to hang up on superficial stereotypes but metal is sophisticated too -- a lot of the voicing/structure/styling is so classical-and-jazz that, with instrument switches, it can be indistinguishable. Don't get me started on trying to claw my way through metal time signatures