In the preparations for the release of my book A Hundred Reasons to Run 100km next month, I created a page for it and thought it would be neat to include a list of 100km races worldwide. As I type, I know there's one happening in Centennial Park in Sydney, Australia, aptly named the Centennial Park Ultra.
The course consists of a relatively flat 3.8km lap that I only know too well, as I did a lot of my training (running and cycling) there from late 2000 until late 2007. My former triathlon coach who had us training there is running the 50km event.
In compiling my list, I looked at various websites including ULTRAmarathonRunning.com, Ultrasignup.com and UltraRunning.com. You'll find the list of 100km races around the world here.