This is a Japanese martial art that I found fascinating and a mental challenge as much as a physical challenge. It's based on avoiding conflict, evading your attacker's momentum and taking advantage of the ensuing weakness and imbalance. You can travel to seminars in different parts of the country and even the world, meeting some great people on the way.
Although I personally no longer train, I treasure my memories from my times on the mat.
For more information, visit the home page of my old organisation or my friend Mark's club website.