Angels Landing, a rock formation 1488 feet high, Zion National Park, Utah, United States of America

Angels Landing, a rock formation 1488 feet high, Zion National Park, Utah, United States of America

Ben Mor Coigach in winter, Assynt, Assynt-Coigach National Scenic Area, Sutherland, Scottish Highlands, Scotland, United Kingdom, Europe

Hiker on Maja Jezerce, standing at 2,694 metres (8,839 ft) above the Adriatic, the highest peak in the high Dinaric Alps, Albania, Europe

View from the Summit of Mulhacen over the Sierra Nevada, Andalusia, Spain, Europe

Hiking trail along rugged arid mountain valley of the Sierra Nevada, with Alcazaba in the distance, Andalusia, Spain, Europe

View of Jamestown from the top of Jacob's Ladder on Saint Helena, South Atlantic Ocean

Fisheye view from below the fire watchtower on summit of Apache Maid Mountain, Coconino National Forest, Arizona, United States of America

Coconino National Forest from the southwest summit of Apache Maid Mountain, Coconino National Forest, Arizona, United States of America

Hiking trails around Seven Rila Lakes, Bulgaria, Europe

View of Jamestown from the top of Jacob's Ladder on Saint Helena, South Atlantic Ocean

Looking towards Pen-y-Fan, Brecon Beacons, Powys, Wales, United Kingdom, Europe

The 17th switchback along the North Kaibab Trail at Grand Canyon North Rim, UNESCO, Arizona, United States of America

Passenger train moving away on unique circular curving portion of spiral track around a hill in order to gain elevation, Demodara Loop, at Demodara Railway Station in hill country of Sri Lanka

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.