What's your hobby? Or, rather, do you call your interests or passions hobbies at all, or does the word hobby connote something frivolous or strangely obsessive? The term hobby goes back to a nickname for a horse, which transferred to the popular hobby horse toy for children, who'd play with it incessantly, the way one might obsessively fuss over model trains. This is part of a complete episode.
This is, admittedly, an overly modern take, but it seems to me that any activity or subject you read about regularly on the internet -- other than something from which you earn money – is a hobby. If you spend a lot of time on ancestry.com, then genealogy is a hobby for you. If you read all about the latest news from the running world (particularly the gossipy parts), running is a hobby for you. If you have more than one bookmark related to it or regularly read or participate in a forum about it, it's probably a hobby.
I guess this is also true if you read hard copy magazines (like runner's world or guitar player) or regularly have conversations with people about this topic. In short, any activity or subject about which you regularly seek information and/or participate in discussions about would be a hobby to me (again, so long as you're not doing it for financial gain).
All the best,
The thing needs to be serious enough and trivial enough. Rock climbing probably fits as hobby, but mountain climbing probably not. Praying and going to church are too serious.
Physical exercises? Probably not because too many people do it. So 1 more criterion: has to be done by few enough, an esoteric thing. Stars gazing. Doing crossword puzzles, maybe.