I always think this is a funny question because I lead kind of a double life. On one side, I am involved with lots of professional groups, community organizations, private clubs and so forth. I spend so much free time involved with these and networking, I consider them hobby/obligations (hobbligations?). It might sound weird to treat social commitments as hobbies, but my background is solidly in sociocultural anthropology and it's difficult to be in large groups and not deconstruct the whole thing (keeps it much more interesting, assuredly!!). Lots of super nerdy stuff here too (e.g. I keep a Lit. blog and like to crack other languages like codes; I've been on a Scandinavian kick of late).
On the other? I love exploring everything I possibly can - abandoned places, skateboarding in tunnels, climbing mountains for secret caves and waterfalls, scaling cliffs for secret surf spots, jumping off very high places I probably shouldn't, so forth. I still go to a lot of hardcore, punk, thrash//suuubculture shows too.
I don't tend to have a lot of downtime.