My biggest hobby is trying to find the time to do my hobbies...
Martial arts - I teach jujutsu at a local club; started on judo when I was 8, and been studying various arts ever since (the big Five Oh looms next year). Mainly jujutsu since 82.
Amateur dramatics - performing on stage, building sets, making props, writing lyrics. Just auditioned for a part in The Mikado for a production in May.
Playing music - guitar, piano, trumpet. Mostly for my own amusement, although I did a couple of gigs with the guitar last year.
Making things!
Helping out with the local Scout group, teaching outdoorsy stuff and being one of the usual suspects when stuff needs putting up, taking down etc.
Breeding cats - although this is more the Management's hobby than mine

Collecting firewood for the woodburner - possibly more of an obsession than a hobby

Reading: sci-fi, historical, anything really.
Oh, and spending too much time on internet forums
