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Off sites are the cure de jour of team building. Take your team for a trip to a lodge in the mountains and it will come back sans its dysfunction. 
I have been to some excellent off sites. So effective that one feels like a changed person when they get back. Then there are ones that take away a few days of your life away from family and work. Like anything else, it is the planning and execution of the off site that makes a difference.
Here is a dated article but an important one on a different type of offsite. Those of you who remember the go-go 90s, will immediately sense the A-type agenda on this offsite. However, it would be good to take away another point: The agenda and activities of an offsite must fit the organizational culture and leadership style.
I promised you an answer to settle the "which offsite is the best" question. Unfortunately, that is not happening in this article!