Men slide in the mud during the Boryeong Mud Festival at Daecheon Beach in Boryeong, South Korea, Saturday, July 22, 2017. The 20th annual mud festival features mud wrestling and mud sliding. (Photo by Ahn Young-joon/AP Photo)

Female winner Ane Guro Moen at Hardangervidda Marathon on September 2, 2017 in Eidfjord, Norway. Hardangervidda Marathon goes through parts of the National Park of Hardangervidda, passing through glaciers and waterfalls. (Photo by Kai-Otto Melau/Getty Images)

“Himalayan Dog”. This dog just appeared out of nowhere and followed us for an entire week during our trekking trip in the Himalayan outback. He always used to sleep in front of our tent and guarded us in the nights. When I decided to get up at 4 a.m. to climb the next 5000 m peak for sunrise he accompanied me as well. On the top he was sitting for the entire 30 minutes on this place looking straight into the countryside. Photo location: Ladakh, India. (Photo and caption by Sebastian Wahlhuetter/National Geographic Photo Contest)

“Lofoten Glow”. I was desperately searching a good sunrise spot this particular morning. Normally Storvatnet Lake is completely covered in snow, so you can only imagine my surprise when I saw these crazy ice formations almost being shot out of the frozen lake. I put my crampons on and took a big risk walking out. I could hear the ice cracking underneath my feet, and when you’re all alone in a fjord/canyon like this – the cracks are echoed and sound really frightening. Was it worth it? I sure think so! Photo location: Storvatnet, Lofoten Islands in Northern Norway. (Photo and caption by Stian Klo/National Geographic Photo Contest)

Tourists take a “selfie” as demonstrators burn a trash container during a May Day rally in Barcelona, Spain, on May 1, 2014. Tens of thousands of workers marked May Day in European cities with a mix of anger and gloom over austerity measures imposed by leaders trying to contain the eurozone's intractable debt crisis. (Photo by Manu Fernandez/Associated Press)

A young Thai man jumps in the air and cheers as his rocket takes off at the Bun Bang Fai Rocket Festival on May 10, 2015 in Yasothon, Thailand. (Photo by Taylor Weidman/Getty Images)

A visitor poses for a photograph in front of a 3D painting depicting a Japanese Imperial army soldier at a 3D art gallery in Beijing January 16, 2015. (Photo by Kim Kyung-Hoon/Reuters)

In this image distributed on Tuesday, September 29, 2015, 11-year old dance star Taylor Hatala and friends are seen filming their new Monster High Boo York, Boo York music video #CityGhouls in Los Angeles. (Photo by Casey Rodgers/Invision for Mattel/AP Images)