You are basically running on the moon. When or if you can run, that is. The course is so difficult at times there is no run option. You spend 3 days and 125KM covering the most vicious terrain imaginable. Mohamad Ahansal, 8 time winner of MDS, described the full as the tougher than MDS and it lists itself as the most difficult multi terrain foot race in the world, and I can see why,

Imagine no sleep due to midnight sun, then a bare chested Viking Clap to start the day, before a black volcanic ash road into the distance. The wind hits you like a freight train and you can't hear the music from your earphones. A turn you and you are climbing up a 45 degree incline to a ridge on volcanic skree that means one step forward is met with a slide back. From the top the valley below looks like mud but is 5 inch deep volcanic ash that is like running on sand. The next valley is long grass that no one has run on before so there are no paths at all. Lung burst climbs lead to great views, but then moss covered rocks as far as the eye can see destroys your spirit. It is best to buddy up. The format was 40K day one, 52 day 2 and 33 day 3. I calculated about an 11,000kcalorie deficit for the race as it is just so hard. 

It is amazing, it is unlike anything you are likely to do, or likely repeat. None of the surfaces are easy, you camp, you barely sleep, and the 2 CPs just have water. The sort of people who will run the race with you are the special kind that will tell you its brutal and then want to do it again. Me? Give me chance to process it for a while in therapy and we shall see.