This resource purports to be "The Ultimate Resource of the Independent Traveler." And it is pretty good.
While packaged vacations to warm beaches or mainstream places like Disneyland are always fun and predictable, it's great to push the limits with yourself and see what else exists in this world. You would be surprised at the variety that exists and how affordable these adventure trips are compared to a standard vacation to, say, Mazatlan, Mexico. Be curious, test yourself, and remember what writer Sam Keen said, "To be on a quest is nothing more or less than to become an asker of questions."
This is the basic ideology behind most non-traditional vacations, adventure travel included. Though most adventure travels people experience are offered in similar packages to the "non-adventure" ones, this site reiterates the value of a less structured experience.