I like doing complex things that require your full attention or you die. Stuff like rock-climbing (although I'm too out of shape to do that) Strenuous hiking is great -- wish I did more of it. The trick is that if you have an analytical and goal-intensive mind, like I suppose many of us do, you may have to try some unusual things to beat it into neutral gear.

I've found that even out of shape old farts like me can get the same results by simply raising your pulse to about 80-90% of max for an hour or so. If you do this using smart exercise equipment, it does all the work of figuring out how hard you should be working. Somewhere around minute 20 or so I find myself relaxing mentally, although the physical part is a little painful. Your mind begins to wander. At this point, once you're used to it, you can easily slip into a very meditative state. Focus on a point, recite a mantra, relax your mind. This reminds me of the same feeling I had when I ran, except you don't get the great feeling of being outdoors. On the good side, you don't have to worry about dogs, traffic, or slippery roads.

Best thing about all of that is that you get a great endorphin rush when you're done for the next few hours.

My problem is that I'm always trying to hack my way out of relaxing -- using less time, gulping a Red Bull instead of doing my workout, etc. I'm slowly learning that this isn't something you can take shortcuts with, but it's a lesson I have a hard time with. I guess my mindset is that if you can make a computer do something really cool in ten minutes you should be able to hack your body-mind the same way, but it doesn't work like that.