Pamukkale, Turkey, is home to these terrace pools, formed by the build-up of carbonate mineral from the warm water flowing from the thermal springs above. (Photo by Image Courtesy of Jennifer Hayes/Getty Images)

Wildlife photographer Danté Fenolio has headed into areas untouched by sunlight – deep seas, caves and underground – and found creatures that are exploding with colour. Here: The golden harlequin toad has vanished from the wild, and only a small number live on in captivity. A fungus caused them, and many other amphibians, to die out in their home in Central America. (Photo by Danté Fenolio/The Guardian/Johns Hopkins University Press)

Passengers from a passing train watch as rescue workers search a train which crashed in Karachi, Pakistan, November 3, 2016. At least 17 people have been killed and dozens more injured after two trains carrying hundreds of passengers collided in Pakistan's southern port city of Karachi, officials said. (Photo by Akhtar Soomro/Reuters)

A child stands inside a large soap bubble made by a street artist at the Mayor square in central Madrid, Friday, December 9, 2016. (Photo by Francisco Seco/AP Photo)

“Just hanging out”. As full autumn hits the valley of Hallingdal in Norway, this bear chills out in a tree which seems to barely cover its weight. Photo location: Flå, Hallingdal, Norway. (Photo and caption by Jorgen Tharaldsen/National Geographic Photo Contest)

A thrill-seeking storm chaser captured the precise moment these giant lightning bolts lit up dark skies in a series of incredible storms. (Photo by Craig Eccles/Solent News & Photo Agency)

A photographer has done her best to guess what her dog is daydreaming about – creating a series of fantasy adventures around her unaware pooch as he takes his daily naps. (Photo by Caters News)

“Festive preparation”. Baghnapara, Bardhaman, West Bengal, India. Two girls prepare for the Gajan festival. They will perform a play based on Indian mythology. (Photo by Krishnasis Ghosh)