“The Challenge!” Young boy relishes in a game of tug of war before school. Photo location: Lake Titicaca, Peru. (Photo and caption by Paul Heyman/National Geographic Photo Contest)

Miniature spring-wound 35-mm film camera in a modified cigarette pack. The Tessina’s small size and quiet operation provided more options for concealment than most commercially available models. (Photo by Central Intelligence Agency)

A firefighter uses a saw to open a metal gate while fighting a fire in a convenience store and residence during clashes after the funeral of Freddie Gray in Baltimore, Maryland in the early morning hours of April 28, 2015. (Photo by Eric Thayer/Reuters)

Sandra, a 29-year-old orangutan at Buenos Aires' zoo, on May 20, 2015. Sandra got cleared to leave a Buenos Aires zoo that was her home for 20 years, after a court ruled she was entitled to more desirable living conditions. (Photo by Juan Mabromata/AFP Photo)

A new book published by the UK Natural History Museum showcases some of the most memorable underwater photographs taken over the last few decades in its annual wildlife photographer of the year competition. Here: Giant gathering by Tony Wu. “The first indication that something extraordinary was going on were the blows, huge numbers of them – the exhalations of huge numbers of whales. Entering the water, the photographer witnessed an extraordinary scene”. (Photo by Tony Wu/Unforgettable Underwater Photography/NHM)

World's Greatest Swimming Pools: Four Seasons, Serengeti Pool, Tanzania. A show of elephants, buffalo and baboons awaits thanks to an active watering hole below the free-form infinity pool at this plush hideaway inside Serengeti National Park. Bonus: Because of infrared technology at the hole, guests can be notified on their bedroom TV when animals are approaching. When you've got word of wildlife on the horizon, catch them from your private terrace – or head back to the pool. (From $1,650). (Photo by Four Seasons)

A man grimaces walking by the “Lettuce Ladies”, a group of PETA activists, during an event promoting a vegan lifestyle, downtown Bucharest, Romania, Monday, August 14, 2017. Two PETA vegan ambassadors distributed vegan food to passers by in the Romanian capital, the latest stop in a tour including the United States, Russia and Turkey aimed at promoting a vegan lifestyle. The sign reads in Romanian “start fresh: become vegan”. (Photo by Andreea Alexandru/AP Photo)

Women perform under black fabric during a street performance in Pristina on October 6, 2017 against sexual harassments in Kosovo. (Photo by Armend Nimani/AFP Photo)