Brazilian Jiu Jitsu - It's an odd combination of intense physical activity and human chess (setting up attacks in advance while also trying to deflect your opponents attacks, except using chokes or joint breaks). Grapplers are either freak athletes, 120lb stoners, or business professionals. BJJ is one of the most unique sports/martial arts out there, and I encourage everyone to try it at least once.

I started after enrolling my children in it, and then figuring "why the hell not, I should train too."