If that kind race looks interesting, but you are not an ultra-marathoner, check out orienteering: http://www.mensjournal.com/adventure/outdoor/the-rise-of-ori....

It's basically a land navigation race. The club I'm in, (http://mnoc.org), does courses that are usually 3km to 8km in length (there will be several to choose from).

The events are pretty minimalist compared to obstacle races like Warrior Dash, mud runs, ect. It's just you, a map, and a large chunk of woods.