Go arctic! I didn't get to do this (below), but I did get to go to AK for the first time for my birthday in January...Fairbanks. I am dying to go back...there is an enormous system of trails with cabins there that you can Xcountry ski into. But, check out the site below. It looks really intriguing.
http://www.alaskaultrasport.com/tours_trips/Trips.html
Or, for something completely different (you mentioned schools):
http://www.thecoaches.com/coactive.html
I don't know your background, but this introductory coaching course is a weekend thing, and works as a stand alone course that, in my opinion, will enhance just about anything you're doing, and stretch you a bit in the process. Some folks would be challenged more than others, depending on personality and background, but this is a neat course. They have them all over the place, so you could travel to one and incorporate other things into your birthday trip, too.
Whatever you do, have a great time, and good for you for celebrating your own birthday!
"The best rides are the ones where you bite off much more than you can chew, and live through it." ~ Doug Bradbury