The best team building exercise I've seen

At a previous job, my manager did one of the best team building exercises I know of.
He purchased the biggest kite he could find and organized a kite flying picnic lunch for the whole IT department.
The kite was something like 5 feet by 9 feet that required 500 pound test line. To fly this kite, we needed a group effort at every stage. Two people had work gloves, so they both held the line. It took two people to hold the kite up to get it in the air.
Someone had the idea to tie a digital camera to the string and have it record the flight. A person had to hold the camera as we ran with the kite and the line to get it in the air.
Once in the air, the kite was a challenge to hold on to. It had enough pull to lift me to my toes. The kite took another team effort to keep it in control. We let the kite out several hundred feet and tied the line to a tree.
We ate lunch and relaxed for a while.
It took another group effort to bring the kite in.
There were two people who stood on the line, one backing the other up. Then they guys wearing gloves would pull the kite down about 50 feet one of the guys would stand on the line. Then the glove guy would zig the line down another 50 feet and the other guy would stand on it. It took a lot of work.
Lastly, my manager rigged a cordless power drill to the spool and used it to reel the line from the ground onto the spool.
When we got back to the office we watched the movie from the camera. It was a really cool experience.
I think what made this such a great team building experience is that it wasn't planned as such. It was a fun activity that required teamwork but it didn't purport to be one of the contrived team building outings that often fail to meet their goals.