Ultra- trailers compete at sunrise on September 2, 2017 in Courmayeur, Italy, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. The 15 th Ultra- Trail du Mont- Blanc (UTMB) is a mountain ultramarathon with numerous passages in high altitude (>2500 m) and in difficult weather conditions (night, wind, cold, rain or snow). (Photo by Jeff Pachoud/AFP Photo)

“At her job, Maria Torero cares for sick human beings. At home, she lavishes love on slowly dying cats – 175 of them at last count. The 45-year-old nurse has turned her two-story, eight-room apartment into a hospice for cats with feline leukemia, scattering it with scores of feeding dishes and at least two dozen boxes litter boxes. Some have suggested she shelter healthy cats instead. “That's not my role”, she told The Associated Press. “I'm a nurse. My duty is to the cats that nobody cares about”. She said that “people don't adopt adult cats, especially if they are terminally ill”. – Franklin Briceno via Associated Press. (Photo by Martin Mejia/AP Photo)

Senji Nakajima sleeps with his Love Doll “Saori” at Love Hotel on June 4, 2016 in Nagano, Japan. Senji Nakajima, 61 years old, lives with his life-size “love doll” named “Saori” in his apartment in Tokyo, Japan. Nakajima, married with two children, who lives away from home for work, first started his life with Saori six years ago. (Photo by Taro Karibe/Getty Images)

Roof-topping enthusiast Daniel Lau takes a selfie with high-rise buildings down below as he stands on the top of a skyscraper in Hong Kong, China on August 15, 2017. A craze that began in Russia has now taken hold in Hong Kong, one of the world's most vertical cities. Mr Lau said he had been inspired by Russian climbers and that he was unafraid of the vertiginous heights he scales. (Photo by ImagineChina/Rex Features/Shutterstock)

“Secrets of the Whales”. Skerry’s photographs celebrate the lives and culture of whales, illuminating recent research and their diverse behaviours. His latest work focuses on four key species: sperm whales, humpbacks, orca and beluga whales. Humpback whales bubble-net feeding off the coast of Alaska. They work cooperatively to feed on herring by blowing a perfect ring of bubbles underwater to form a net encircling the fish. The whales then swim up through the centre of the bubble net with their mouths open. (Photo by Brian Skerry/National Geographic Photo/Visa pour l'Image)

A firefighter holds a red panda (Ailurus fulgens) from its tail while removing it from a tree at a residential area in Kunming, Yunnan province, July 3, 2014. The animal was spotted in the residential area and was brought down from the tree after residents reported its sighting to the police, local media reported. (Photo by Reuters/Stringer)

Wedges of an orange generate enough current and electrical juice – 3.5 volts – to power an LED. The fruit’s citric acid helps electrons flow from galvanized nails to copper wire in this 14-hour exposure. This image was published in September’s Visions of Earth, a trio of photos that appear in each issue of National Geographic. (Photo by Caleb Charland/National Geographic)