Thor's Hammer from the Navajo Loop Trail, Bryce Canyon National Park, Utah, USA

Hoodoos strongly lit by early morning sun with heavy cloud, Peekaboo Loop Trail in winter, Bryce Canyon National Park, Utah, United States of America, North America

Distant view with cloud layers from elevated position on Peekaboo Loop Trail in winter, Bryce Canyon National Park, Utah, United States of America, North America

Hiker in front of Wall of Windows lit by early morning sun, icy Peekaboo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

Wall of Windows lit by early morning sun, with snowy Peekaboo Loop Trail, Bryce Canyon National Park, Utah, USA

Hiker takes a break on the Peekaboo Loop Trail in winter, with snowy red rocks and cliffs, Bryce Canyon National Park, Utah, United States of America, North America

Large hoodoo lit by early morning sun, with snow and pine trees, Peekaboo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

Hoodoos strongly lit by early morning sun with heavy cloud, Peekaboo Loop Trail in winter, Bryce Canyon National Park, Utah, United States of America, North America

Snow clearing equipment at a tunnel through sunlit red rock in winter, Peekaboo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

Wall of Windows from base in early morning sun, snow and pine trees, Peekaboo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

Icy Peekaboo Loop Trail with hoodoos, trees and snow in the early morning, Bryce Canyon National Park, Utah, United States of America, North America

Hoodoos and snow with layers of cloud, from Peekaboo Loop Trail in winter, Bryce Canyon National Park, Utah, United States of America, North America

Peekaboo Loop Trail switchbacks wind through hoodoos lit by early morning sun in winter, Bryce Canyon National Park, Utah, United States of America, North America

Wall of Windows lit by early morning sun, silhouetted rock, Peekaboo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

Peekaboo Loop Trail sign with snow and rocks lit by early morning winter sun, Bryce Canyon National Park, Utah, United States of America, North America

The Queens Garden from Navajo Loop Trail, Bryce Canyon National Park, Utah, USA, North America

View of Thor's Hammer from the Navajo Loop Trail in Bryce Canyon National Park, Utah, United States of America, North America

High angle view of Boulder Creek, the Watson Lake Loop Trail crosses this creek, Prescott, Arizona, United States of America, North America

High cliffs towering above the Navajo Loop Trail below Sunset Point, Bryce Canyon National Park, Utah, United States of America, North America

Colourful rock formation in the Queen's Garden beside the Navajo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

Two hikers heading down the Navajo Loop Trail below Sunset Point, Bryce Canyon National Park, Utah, United States of America, North America

A divide in the trail loop for the Giant Logs trail at Petrified Forest National Park with the Rainbow Forest Museum on upper left, Arizona, United States of America, North America

Panorama South view of Courthouse Butte and the Judges Bench from Courthouse Butte Loop Trail in Sedona, Arizona, United States of America, North America

View of Thor's Hammer from the Navajo Loop Trail in Bryce Canyon National Park, Utah, United States of America, North America

Woman in Desert Loop Trail in Carlsbad Caverns National Park, New Mexico, United States of America, North America

Man enjoying the view along The Petrified Forest Loop Trail inside Theodore Roosevelt National Park, North Dakota, United States of America, North America

Woman hiking along The Petrified Forest Loop Trail inside Theodore Roosevelt National Park, North Dakota, United States of America, North America

View of hoodoo formations from the Navajo Loop Trail in Bryce Canyon National Park, Utah, United States of America, North America

View of hoodoo formations from the Navajo Loop Trail in Bryce Canyon National Park, Utah, United States of America, North America

Beautiful sight on The Petrified Forest Loop Trail inside Theodore Roosevelt National Park, North Dakota, United States of America, North America

The Village of Oak Creek on the south side of Sedona viewed from the Airport Loop Trail, Arizona, United States of America, North America

View of hoodoo formations from the Navajo Loop Trail in Bryce Canyon National Park, Utah, United States of America, North America

Cathedral Rock at the intersection of upper Baldwin Loop and HiLine Trails with sign warning that the HiLine Trail is for experts only, Sedona, Arizona, United States of America, North America

Panorama of Bell Rock and Courthouse Butte, viewed from Big Park Loop Trail, Sedona, Arizona, United States of America, North America

Snowy cliffs from Peekaboo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

Beautiful sight on The Petrified Forest Loop Trail inside Theodore Roosevelt National Park, North Dakota, United States of America, North America

Gorge with natural arch by Navajo Loop Trail, Bryce Canyon National Park, Utah, USA

Hiker on Navajo Loop Trail with hoodoos and pine trees lit by early morning sun in winter, Bryce Canyon National Park, Utah, United States of America, North America

Thor's Hammer from the Navajo Loop Trail on a partially cloudy day, Bryce Canyon National Park, Utah, United States of America, North America

Popular rock formation (hoodoo) named Thor's Hammer taken from Navajo Loop Trail, Bryce Canyon National Park, Utah, USA

Navajo Loop trail descending from Sunrise Point, Bryce Canyon, Utah, United States of America, North America

View of The Amphitheater from the Navajo Loop Trail in Bryce Canyon National Park, Utah, United States of America, North America

Snowy cliffs from Peekaboo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

Hoodoos lit by early morning sun in winter, Peekaboo Loop Trail, Bryce Canyon National Park, Utah, United States of America, North America

The zigzag climb of the beautiful Navajo Loop Trail in Bryce National Park, Utah. United States

Rock formation Thors Hammer, morning light, snow-covered bizarre rock landscape with Hoodoos in winter, Navajo Loop Trail, Bryce Canyon National Park, Utah, USA, North America

Rock formation Thors Hammer, morning light, bizarre snowy rock landscape with Hoodoos in winter, Navajo Loop Trail, Bryce Canyon National Park, Utah, USA, North America

Morning light, snow-covered bizarre rocky landscape with Hoodoos in winter, Navajo Loop Trail, Bryce Canyon National Park, Utah, USA, North America

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.

Hikers descend into Surprise Valley to access the lower canyon through a break in the 400-foot-tall Redwall on the Thunder River Trail in the Grand Canyon outside of Fredonia, Arizona November 2011. The 21.4-mile loop starts at the Bill Hall trailhead on the North Rim and descends 2000-feet in 2.5-miles through Coconino Sandstone to the level Esplanada then descends further into the lower canyon to access Thunder River, Tapeats Creek and Deer Creek.

Hikers on the sandstone Esplanade of the Thunder River Trail below the North Rim of the Grand Canyon outside Fredonia, Arizona November 2011. The 21.4-mile loop descends 2000-feet in 2.5-miles through Coconino Sandstone from the Bill Hall trailhead to connect the Thunder River and Deer Creeks trails. Hikers descend into the lower canyon through a break in the 400-foot-tall Redwall to access Surprise Valley, Deer Creek, Tapeats Creek via Thunder River and even the Colorado River.

Douglas Fir trees stand tall in the Wall Street section of the Navajo Loop trail in Bryce Canyon National Park.

Woman rides the Submarine Rock Loop in South Sedona, Arizona. The trail has everything from slickrock to single track to stairs that lead to Submarine Rock.

Hikers on the sandstone Esplanade of the Thunder River Trail below the North Rim of the Grand Canyon outside Fredonia, Arizona November 2011. The 21.4-mile loop descends 2000-feet in 2.5-miles through Coconino Sandstone from the Bill Hall trailhead to connect the Thunder River and Deer Creeks trails. Hikers descend into the lower canyon through a break in the 400-foot-tall Redwall to access Surprise Valley, Deer Creek, Tapeats Creek via Thunder River and even the Colorado River.

Rose Cowles runs through the fall leaves on the Boogerman Loop trail in the Cataloochee area of the Great Smoky Mountains National Park, NC

Hikers on the sandstone Esplanade of the Thunder River Trail below the North Rim of the Grand Canyon outside Fredonia, Arizona November 2011. The 21.4-mile loop descends 2000-feet in 2.5-miles through Coconino Sandstone from the Bill Hall trailhead to connect the Thunder River and Deer Creeks trails. Hikers descend into the lower canyon through a break in the 400-foot-tall Redwall to access Surprise Valley, Deer Creek, Tapeats Creek via Thunder River and even the Colorado River.

Woman rides the Submarine Rock Loop in South Sedona, Arizona. The trail has everything from slickrock to single track to stairs that lead to Submarine Rock.

Lupine flowers along the Lupine Loop Trail with the town of Crested Butte, Whetstone Mountain adn the Slate River in the background, Colorado.

Woman rides the Submarine Rock Loop in South Sedona, Arizona. The trail has everything from slickrock to single track to stairs that lead to Submarine Rock.

Woman rides the Submarine Rock Loop in South Sedona, Arizona. The trail has everything from slickrock to single track to stairs that lead to Submarine Rock.

A woman mountain biking past wildflowers on the Lupine Loop Trail in Crested Butte, Colorado.

A young girl mountain biking past wildflowers on the Lupine Loop Trail in Crested Butte, Colorado.

Woman rides the Submarine Rock Loop in South Sedona, Arizona. The trail has everything from slickrock to single track to stairs that lead to Submarine Rock.

Icon, information sign post at Cedars Mill Trail in Lynn Valley Canyon, North Vancouver, British Columbia, Canada

State Of Hawaii Division Of Forestry And Wildlife Headquarters At Makiki Loop Trail, Oahu, Hawaii, United States Of America

Makiki Loop Trail, With Sign Showing Direction To Trail Head, Oahu, Hawaii, United States Of America

Navajo Loop Trail, Tall dead trees and rocks against clear sky, USA, Utah, Bryce Canyon

Navajo Loop Trail, Tall Douglas Fir trees, USA, Utah, Bryce Canyon

Navajo Loop Trail, Tall Pine trees, USA, Utah, Bryce Canyon

Navajo Loop Trail, Pine tree and rock, USA, Utah, Bryce Canyon

Navajo Loop Trail, Tall dead trees and rocks against clear sky, USA, Utah, Bryce Canyon

Navajo Loop Trail, Tall Pine trees, USA, Utah, Bryce Canyon

Navajo Loop Trail, Tall Pine trees, USA, Utah, Bryce Canyon

Navajo Loop Trail, Tall Douglas Fir trees, USA, Utah, Bryce Canyon

Navajo Loop Trail, Tall Douglas Fir trees, USA, Utah, Bryce Canyon

Navajo Loop Trail, Cracked rock, close-up, USA, Utah, Bryce Canyon

Navajo Loop Trail, Tall Douglas Fir trees, USA, Utah, Bryce Canyon