South African endurance athletes Ryan Sandes and Ryno Griesel are no strangers to running across challenging terrain. The duo recently ran the entire border of Lesotho (pictured) in 16 days. <strong>Look through the gallery to see more of the world's most extreme foot races.</strong>
South African endurance athletes Ryan Sandes and Ryno Griesel are no strangers to running across challenging terrain. The duo recently ran the entire border of Lesotho (pictured) in 16 days. Look through the gallery to see more of the world's most extreme foot races.
Craig Kolesky / Red Bull Content Pool
<strong>Everest: </strong>It's hard to imagine climbing Mount Everest -- let alone running it. But that's what hundreds of marathon runners have been doing each year since 2003. Pictured: runners compete in the Everest Hillary Marathon across Everest's Base Camp, in 2006.
Everest: It's hard to imagine climbing Mount Everest -- let alone running it. But that's what hundreds of marathon runners have been doing each year since 2003. Pictured: runners compete in the Everest Hillary Marathon across Everest's Base Camp, in 2006.
Bikash Karki/AFP/Getty Images
<strong>Everest:</strong> The world's highest marathon, runners begin at Base Camp (elevation 5,364 meters) and end at in the Nepalese town of Namche Bazar.
Everest: The world's highest marathon, runners begin at Base Camp (elevation 5,364 meters) and end at in the Nepalese town of Namche Bazar.
Bikash Karki/AFP/Getty Images
<strong>Iditarod Trail:</strong> Everest isn't the only cold-weather trail. In Alaska, endurance runners complete in the 350-mile (563 kilometers) Iditarod Invitational Race, following the <a target="_blank" target="_blank">same path</a> as the iconic sled dog race.
Iditarod Trail: Everest isn't the only cold-weather trail. In Alaska, endurance runners complete in the 350-mile (563 kilometers) Iditarod Invitational Race, following the same path as the iconic sled dog race.
Dan Bailey/Design Pics/ZUMA Press
<strong>Morocco:</strong> From the snow to the sand, the Marathon des Sables in Morocco's Sahara Desert is a grueling race against the heat. Here, runners take part in the third stage in March 2022.
Morocco: From the snow to the sand, the Marathon des Sables in Morocco's Sahara Desert is a grueling race against the heat. Here, runners take part in the third stage in March 2022.
Jean-Philippe Ksiazek/AFP/Getty Images
<strong>Morocco: </strong>Pictured: runners compete in stage four, which comprises of nearly 86 kilometers (53 miles) over two days. In total, the race covers 250 kilometers (186 miles) in one of the world's harshest climates. The race is billed as the "<a target="_blank" target="_blank">toughest footrace on Earth</a>."
Morocco: Pictured: runners compete in stage four, which comprises of nearly 86 kilometers (53 miles) over two days. In total, the race covers 250 kilometers (186 miles) in one of the world's harshest climates. The race is billed as the "toughest footrace on Earth."
Jean-Philippe Ksiazek/AFP/Getty Images
<strong>Peru:</strong> The Half Marathon des Sables race through the Ica Desert in Peru also pits athletes against extreme conditions. Despite being called a half marathon, the distance is actually up to 120 kilometers (75 miles), split into multiple stages across the desert landscape.
Peru: The Half Marathon des Sables race through the Ica Desert in Peru also pits athletes against extreme conditions. Despite being called a half marathon, the distance is actually up to 120 kilometers (75 miles), split into multiple stages across the desert landscape.
Martin Bureau/AFP/Getty Images
<strong>The Alps:</strong> The annual mountainous ultramarathon of the Ultra-Trail of Mont-Blanc covers 170 kilometers (106 miles) in the Alps across France, Italy and Switzerland. Runners, such as this competitor in the 2018 iteration, face a variety of challenging conditions from snow and wind to the darkness of night, all while making several passes through high altitude.
The Alps: The annual mountainous ultramarathon of the Ultra-Trail of Mont-Blanc covers 170 kilometers (106 miles) in the Alps across France, Italy and Switzerland. Runners, such as this competitor in the 2018 iteration, face a variety of challenging conditions from snow and wind to the darkness of night, all while making several passes through high altitude.
Jeff Pachold/AFP/Getty Images
<strong>Oman: </strong>The Ultra-Trail of Mont-Blanc also has an Oman event, featuring "<a target="_blank" target="_blank">the majestic heights of Oman's mountainous interior</a>." Swiss runner Diego Pazos (pictured) finished second in the 137-kilometer (85 miles) marathon's inaugural event in 2018.
Oman: The Ultra-Trail of Mont-Blanc also has an Oman event, featuring "the majestic heights of Oman's mountainous interior." Swiss runner Diego Pazos (pictured) finished second in the 137-kilometer (85 miles) marathon's inaugural event in 2018.
Giuseppe Cacace/AFP/Getty Images
<strong>The Amazon: </strong>Dense jungle is not exactly primed for a foot race, but that hasn't stopped runners from traversing the Amazon in Brazil's Jungle Marathon. Here, an endurance athlete competes in 2013, when the race covered 245 kilometers (152 miles) in seven days.
The Amazon: Dense jungle is not exactly primed for a foot race, but that hasn't stopped runners from traversing the Amazon in Brazil's Jungle Marathon. Here, an endurance athlete competes in 2013, when the race covered 245 kilometers (152 miles) in seven days.
London News Pictures/Shutterstock
<strong>The Amazon: </strong>The terrain of the jungle also calls for the occasional water crossing. Pictured: Great Britain's Amy Gasson swims across a river during the ultramarathon in 2014.
The Amazon: The terrain of the jungle also calls for the occasional water crossing. Pictured: Great Britain's Amy Gasson swims across a river during the ultramarathon in 2014.
Alexander Beer/Lnp/Shutterstock
<strong>La Reunion island: </strong>More dense forest awaits runners (such as this competitor in 2019) in the Grand Raid de la Reunion ultramarathon race, on the island of La Reunion in the Indian Ocean.
La Reunion island: More dense forest awaits runners (such as this competitor in 2019) in the Grand Raid de la Reunion ultramarathon race, on the island of La Reunion in the Indian Ocean.
Richard Bouhet/AFP/Getty Images