Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)

An Orthodox priest conducts a blessing in front of the Soyuz TMA-20M for the next International Space Station (ISS) crew, comprised of Jeff Williams of the U.S. and Oleg Skriprochka and Alexey Ovchinin of Russia, at the launchpad at the Baikonur cosmodrome, Kazakhstan, March 17, 2016, ahead of its launch scheduled on March 19. (Photo by Shamil Zhumatov/Reuters)

Behaviour: Mammals category. Giant Gathering by Tony Wu, USA. Dozens of sperm whales mingled noisily off Sri Lanka’s northeast coast, stacked as far down as Tony could see. This was a congregation of dozens of social units, like a gathering of the clans. Aggregations like this could be a critical part of the whales’ rich social lives but are rarely reported. Some two thirds of the population was wiped out before commercial whaling was banned in 1986. This kind of major gathering could be “a sign that populations are recovering”, says Tony. (Photo by Tony Wu/Wildlife Photographer of the Year 2017)

A high-kicking Parisian can-can dancer. (Photo by Hulton Archive/Getty Images). 1895

A goat named “White On The Right” bleats as it is paraded with other goats prior to a race during the annual Easter goat racing event at the Mount Pleasant recreation ground in Tobago April 6, 2015. (Photo by Andrea De Silva/Reuters)

A resident types a text message on her mobile phone, as she sits on a bench made from a tree, which is a creation by Brazilian artist Hugo Franca at Largo da Batata square in Sao Paulo March 17, 2015. Franca, a designer from Sao Paulo is working with the city to make use of fallen trees to turn them into sculpture furniture to line the city's parks, streets and plazas. Brazil's largest city was slammed by several strong storms this rainy season that brought with them heavy rain, lightning and winds as high as 90 kilometres (55 miles) per hour. (Photo by Nacho Doce/Reuters)

David Jackson (C), who voted for Donald Trump, has a discussion with Ryan Graves (L) and Anna Kaminski (R) visiting from Oamaha, Nebraska during a rally against the election of Republican Donald Trump as President of the United States in downtown Indianapolis, Indiana, U.S., November 12, 2016. (Photo by Clay Lomneth/Reuters)

A little girl holding her newborn sister waits for their turn in a queue during a vaccination campaign under the supervision of the Syrian Arab Red Crescent (SARC) humanitarian nonprofit organization, in the besieged Syrian town of Douma, Syria, 23 May 2017. According to a statement from SARC, in the city of Douma some 12,809 children under the age of five were immunized in a vaccination campaign to prevent measles and poliomyelitis. The campaign was the first of its kind with the participation of 100 volunteers. SARC has been delivering vaccines to 17 health centers approved for vaccination campaigns in towns and villages in the Eastern Ghouta area. (Photo by Mohammed Badra/EPA)