Running on bridges
Runners hate bridges. These unwelcome structures spring up like big hills, sometimes slippery, often with open air surfaces that reveal the long drop below. They disrupt the rhythm of a well-designed course.
But what if the entire race was on a bridge? That would be different - and alluring.
The Mackinaw Memorial Bridge Race, in Mackinaw City MI, starts in a park on one side of a long, famous bridge and ends at race headquarters beyond the opposite end of the span.
The course is 5.4 miles long. It doesn't matter that it's not an officially recognized distance. The whole point is to run across THIS bridge.
Race organizers also make a point of banning walkers and strollers and warning runners of the incline at the beginning (I don't think the warning is really necessary).
If you have a unique geographic feature in your area, try to incorporate it into the race. It will add to the attraction of your event.