- Geocaching - I can't believe I forgot this one. It's gaining in popularity, but for now it's sufficiently obscure.
- LEGO building - This is sort of borderline. I guess most people don't realize there are adults who have this as a serious hobby, so that qualifies it as obscure.
- Underwater Hockey - This is a great one. I'd never heard of it or even imagined it. Rather neat.
- Power Kites - Jeph Stahl mentioned this. I actually had the opportunity to try this out, years ago, in grad school, and it had quite an impact, literally. These are kites that are shaped like airfoils which mean they produce a huge amount of lift. My one experience with this, it dragged me across the beach and actually knocked me out. It also caused temporary amnesia of the preceding 6 hours. The kites are pretty cool, and for that matter, temporary memory loss is a sort of cool, if a bit disturbing experience to have. Once.
- Chess Boxing - I saw a link to this, which was the actual inspirating for me posting this additional list. I like the idea of alternating rounds of boxing and chess, but it's a slight shame there is no interaction in the two events, other than the fact that I assume it's harder to concentrate on chess after being hit in the head repeatedly.
- Contradancing - Again, I'm not quite sure if this qualifies. There are a wide range of forms of obscure dance. Most people are aware of square dancing or folk dancing in general, but Contradancing (while very similar to square dancing) seems to qualify to me. Plus, I have many fond memories of contradancing in the late 80s.
So, the total list is now up to 11: German Board Games, Disc Golf, Fly Ball, Change Ringing, Puzzle hunting, Geocaching, LEGO building, Underwater Hockey, Power Kites, Chess Boxing and Contradancing. What else?