Marathon des Sables, or MdS, is a seven-day, about 257 km ultramarathon, which is approximately the distance of six regular marathons. The longest single stage was 91 km long.
This multiday race is held every year in southern Morocco, in the Sahara Desert. Some runners regard it as one of the toughest foot races on Earth. The first event of the Marathon started in 1986. From Wikipedia
