My submission is the Grouse Grind in Vancouver. It's really more of a hike than a run but you've got to try this 2.9km, 853m vertical elevation change trail. Like the marathon, you've got to do it once just to figure out what it is all about. Well marked trail, great view from the top and you take the gondola down. Expect to take at least your 10k time to complete in a hurry or 80 minutes if you take your time. Just ask for directions to Grouse Mountain - 10 minutes from downtown Vancouver.