Juggle. It's about pattern, space and structure, so it tends to suit technically minded people. At the same time, you really can't think of anything else when you're learning a new pattern or trick. You need to get to a zen(ish) state, not thinking, not feeling, not sensing, but being the structure.

Well, at some level.

It's also surprisingly good for the muscles and breathing, and it's been proven to make your brain grow in both grey matter (the cells) and white matter (the connections).

It's also said to improve co-ordination, peripheral vision, reactions, and balance.

Poi is similar. I think there's a continuum that connects several circus arts — as you go from juggling to poi/flag swinging to meteors to short staff to long staff, you lose freedom of motion in exchange for more regular patterns. It's hard to learn one of the circus arts without learning about all of them.

Rock climbing. Requires constant awareness of your surroundings and problem solving(path selection etc.)

Hey great question which is coming up with some interesting answers.

I too do a bit of beekeeping but mountain biking is my main passion.

@RiderOfGiraffes nails it when he says you need to get into that zenish state. It happens when what you are doing requires total commitment and concentration. Riding a log 1m off the ground or going into a big jump does that for me. And afterwards I always feel refreshed and ready to get back into it (usually with a raft of solutions that wouldn't have come to me otherwise).

It doesn't need adrenalin though. I can't get into running because it gives me too much time to think, but try orienteering, which gives you something to think about.

And if you're trying to get into the zone of not thinking doing whatever it is your doing and you're on your own I always find an ipod on reasonably loud volume helps silence the other noises in your mind.

Have you considered Beekeeping?

Checkout Backwards Beekeepers: http://beehuman.blogspot.com/ . They are a group of natural (no chemicals) urban beekeepers. You'll be helping the environment and you might even get some honey out of it.

This is exactly the unusual type of suggestion I was hoping for, beekeeping has never crossed my mind but I'll definitely look into it, thanks.

Acquire a really high level of fitness, the domain space is really large, interesting and rewarding. For example, obviously you need to learn plenty about nutrition, then in order to make it meaningful you need to learn about cooking, then you want to work on your endurance, flexibility, muscle tone and strength, which means learning the muscle groups, then learning how each of the different gym machines will enhance your various objectives, then learning the various stretches for different muscle groups... its intellectual and rewarding. Anecdote: my personal trainer was talking about how an orthopedic doctor is his client, just because he's a doctor doesn't (apparently) mean he's mastered all of these domains.

My nerdy hobbies are origami and poi. I like them because I like thinking about systems, and they provide a structure for improvisation (you could call it hacking if you wanted to).

http://flickr.com/groups/origamitessellations/

http://flickr.com/groups/corrugation/

http://en.wikipedia.org/wiki/Poi_(performance_art)#Modern_po...

I like memory sports like memorizing decks of playing cards, Pi, mental calendar calculation, etc. It's done mostly offline but I use some online gadgets I made to enhance it. It's not physical but if you memorize while running (and collecting mnemonic 'journeys') or working out it's a nice combo. I count my exercise repetitions with the digits of Pi. Ron White trained while in scuba gear. http://www.mindtools.com/memory.html

Despite their gender bias, knitting and needlework are very "hackery" activities. Won't burn calories though :-)

I've found that they don't agree with RSI though... :(

I'm a fan of playing DDR (Dance Dance Revolution). It's kind of an emo-ish game BUT it's fantastic cardio, and in a game structure it's easy to keep the motivation up (I'm a very competitive person, I think that comes with the territory for intelligent people).

I recommend doing something manual, e.g. carpentry or paving. I find it's a great contrast to working in front of a computer. Actually building something tangible is a good feeling. For example, I plan on rebuilding a bicycle wheel this weekend - very relaxing.

Martial arts, preferably medium or full contact. It will make all other physical activities seem boring and it will give you calm and focus that transfers to other aspects of your life.

If that seems like too much, maybe yoga or tai chi.

My current offline activities are guitar and martial arts.

I also studied card magic when I was a teenager. That does wonders for exercising a "hacker" mindset.

Any instrument really is a great switch for the brain after thinking about logic and fitting requirements all day. Reading and improvising music, as well as increasing your own skills on any instrument allows you to use both sides of your brain- feels nice.

I play a lot of golf. It is a really good break for me because it just feels really old school. I don't even bring my cell phone and it is technology free.

i'm kind of enjoying being a saltwater reef aquarium enthusiast, right now. it employs knowledge about a lot of things, from design to chemistry.

Learn to play go! It's the greatest computer-free brain exercise I've ever experienced, by far.

Drawing or sculpture. Dance. Calligraphy. Magic tricks.