The toughest foot race in the world is over 158 miles (254 km) long – more than five times the length of a regular marathon.
Competitors carry all their gear and run over energy-sapping dunes; temperatures can edge over 122°F (50°C); and most runners take six days of pain to reach the finish line. Incredibly, some athletes complete the route in less than 24 hours.
Marathon des Sables, or MdS, (French for Marathon of the Sands, also known as Sahara Marathon) is a six-day, 251 km (156 mi) ultramarathon, which is approximately the distance of six regular marathons. The longest single stage (2009) is 91 km (57 mi) long.
This multiday race is held every year in southern Morocco, in the Sahara Desert. It has been regarded as the toughest foot race on Earth. The first event of the Marathon started in 1986. Wikipedia