OK, so it's not technically a secret. But, if your college or university is located in (or even somewhat near) the northeast quadrant of the USA, it could be the best higher education sustainability conference you've never heard of.
The Northeast Campus Sustainability Consortium puts on a two-day conference every October. This year's conference  is at Princeton, on October 27-28. (The schedule for both days is pretty full, so you might want to travel on the 26th and/or the 29th.)
NECSC is a true grass-roots organization, without so much as its own website. There's a steering committee, and the host school puts up some web pages each year, but without Google the whole thing would be difficult to find. Still, it's as good a "we're all in this together, so let's put our heads together, share information, and help each other keep from doing anything stupid" function as I've ever seen on any subject. Again, take "northeast" figuratively -- last year, there was an attendee from Idaho!
Grass-roots conferences are kind of like church dinners down south. (I haven't always lived in the northeast.) Good folks, good food, nothing fancy, but everything just like it should be. No muss, no fuss, just useful information. And if you really want to know what's going on in town, sit with the old folks.
Anyways, check it out. And post a comment to tell folks about any similar get-together in your neck of the woods!