I spent a month with J. Robinson in Minnesota (a long time ago!) and it remains one of the defining experiences of my life.
http://www.jrobinsonwrestlingcamps.com/wrestling/ This camp is especially useful for wrestlers that need to work on the physicality aspect of wrestling - you will leave in much better shape than you started
Needless to say it is also a test of mental toughness.
It also has great technique, though...