Marathon Ultra Runner Lizzy Hawker running around Bouddha (Boudhanath) (Bodnath) Stupa in Kathmandu, Nepal, Asia

Lizzy Hawker, a world record holding extreme athlete, training on Primrose Hill, London, England, United Kingdom, Europe

Lizzy Hawker, a world record holding extreme athelete, training in London, England, United Kingdom, Europe

Running a trail in the Swiss Alps near Zermatt with a view of Monte Rosa in the distance, Zermatt, Valais, Switzerland, Europe

Running a trail in the Swiss Alps near Zermatt with a view of Monte Rosa in the distance, Zermatt, Valais, Switzerland, Europe

Running a trail in the Swiss Alps near Zermatt with a view of The Matterhorn in the distance, Zermatt, Valais, Switzerland, Europe

Running in the Swiss Alps near Zermatt with a view of Monte Rosa, Zermatt, Valais, Switzerland, Europe

Ultra running in the Swiss Alps near Zermatt, Valais, Switzerland, Europe

Three participants of the UTMB are running in the hills of Chamonix. The famous peaks of the Mont Blanc range are in the background. The Ultra-Trail du Mont-Blanc (also referred to as UTMB) is a single-stage mountain ultramarathon. It takes place once a year in the Alps, across France, Italy and Switzerland. The distance is approximately 166 kilometres (103 mi), with a total elevation gain of around 9,600 m. It is widely regarded as one of the most difficult foot races in Europe. It's certainly one of the largest with over two thousand starters. The combined participation in all of the events is approaching 10 thousand runners. While the best runners complete the loop in slightly more than 20 hours, most runners take 30 to 45 hours to reach the finish line.

An elderly woman is running in the hills of Chamonix. She is close to finishing the extremely exhausting UTMB race. The Ultra-Trail du Mont-Blanc (also referred to as UTMB) is a single-stage mountain ultramarathon. It takes place once a year in the Alps, across France, Italy and Switzerland. The distance is approximately 166 kilometres (103 mi), with a total elevation gain of around 9,600 m. It is widely regarded as one of the most difficult foot races in Europe. It's certainly one of the largest with over two thousand starters. The combined participation in all of the events is approaching 10 thousand runners. While the best runners complete the loop in slightly more than 20 hours, most runners take 30 to 45 hours to reach the finish line.