People in Kathmandu joke that the face mask has now become part of the national dress – an indispensable accessory in an effort to protect themselves from the dust. Nepal has the worst air quality in the world, according to the Environmental Performance Index. (Photo by Pete Pattisson/The Guardian)

Take a look at this stunning photo of Tolbachik, an active volcanic complex on the Kamchatka Peninsula in far eastern Russia. Lava fountains and rivers ran through the area for months after the eruption began with the opening of two Tolbachik fissures in November of 2012. In the midst of this activity, photographers Luda and Andrey (lusika33) took a trip down to see that stunning hell valley on earth. (Photo by lusika33)

American free climber Dean Potter walks on a 41-meter-long and two-centimeter-wide slackline over Enshi Grand Canyon at an altitude of 1,800m on April 22, 2012 in Enshi, Hubei Province of China. Potter successfully finished the lone slackline walk in about three minutes without taking any protective measures. (Photo by ChinaFotoPress/ChinaFotoPress)

Winner of the National Park Foundation's photo contest; Honorable Mention: Fan Favorite. Grand Canyon National Park, Arizona. Three friends enjoy sunrise over the Grand Canyon. (Photo by Peter Blanchard)

This is the incredible moment a fierce lightning bolt crashed against the Grand Canyon illuminating the steep canyon walls. Shrouded in darkness, the breath-taking landscape was shocked into life as mother nature sent the bolt storming down to Earth. As it cracked against the rocks the bright blue bolt illuminated the South Rim of the canyon, considered one of the Seven Natural Wonders of the World. With just the Desert View Watchtower in the foreground, the lightning was perfectly framed by the canyon which is located in Arizona, USA. (Photo by Travis Roe/U.S. Dept. of the Interior/Caters News)

The Mount Bromo volcano erupts in the Bryce Canyon, Utah. (Photo by Reynold Dewantara/2016 National Geographic Travel Photographer of the Year Contest)