I just realised I don't have a hobby :/
I used to paint and draw quite a lot, but since I started studying, I haven't really had much creative energy. All my effort goes into learning which is kind of a hobby in itself, although I don't enjoy the pressure and deadlines.
Like Boobz I used to climb rocks when I wasn't busy analysing their mineral structure, or origin. I really like to go cross-country skiing, but it is obviously difficult in Australia. I like walking in the bush, I enjoy camping and studying nature and animals. Pretty much what I have done all my life, so I wouldn't call it a hobby, more just what I am, or what I always have been drawn to. Because I have these interests, I have never really felt like I needed a hobby.
I started learning the violin for a while and that was great, but the lessons cost too much and I didn't have enough time to practice. I have decided to learn to play Banjo after I finish my studies this year, because not having a creative outlet does affect my sense of calm.