Polar bear twins make their first public appearance with their mother “Freedom” at Ouwehands Zoo Rhenen, in Rhenen, The Netherlands, 19 February 2015. The twins, who were born in November 2014, have not been named because their gender has not yet been determined. (Photo by Bart Maat/EPA)

Participants climb over a wall at the “Tough Mudder” endurance event series in Arnsberg September 6, 2014. Competitors who took part in the endurance event saw themselves having to overcome various military style obstacles. (Photo by Ina Fassbender/Reuters)

Yana Shcherban of Russia looks at the ball after failing to receive it during their FIVB Women's Volleyball World Grand Prix 2014 final round against Japan in Tokyo August 20, 2014. (Photo by Yuya Shino/Reuters)

A woman sits on a terrace at Tiki hostel in Cantagalo favela, in Rio de Janeiro, Brazil, April 16, 2016. Hostels in a few of Rio's more than 1,000 slums serve not only as a cheap housing alternative for the more adventurous among the estimated 500,000 foreign tourists expected to arrive for the Olympics in August. The establishments also open up the rich culture of the city's shantytowns for travellers, giving them a glimpse into once “no-go” areas where about one-fifth of Rio's population lives. (Photo by Pilar Olivares/Reuters)

“Stacked Supercell with Lightning”. This huge mesocyclone supercell was near the Nebraska / Kansas border on the night of June 22nd, 2012. What a stunning structure! (Photo and caption by Jennifer Brindley/National Geographic Traveler Photo Contest)

ATTENTION! All pictures are presented in high resolution. To see Hi-Res images – just TWICE click on any picture. In other words, click small picture – opens the BIG picture. Click BIG picture – opens VERY BIG picture.

Filipinos cross a swelling river in Las Pinas city, south of Manila, Philippines, 09 July 2015. According to the Philippines State weather forecast, heavy rainfall is expected in Metro Manila and nearby provinces due to an enhanced Southwest Monsoon and Tropical Storm Linfa, Typhoon Chan-hom and Typhoon Nangka which are lining up across the Pacific Ocean. (Photo by Francis R. Malasig/EPA)

A young vendor hawks food on a market in Kara in the state of Ogun, on September 23, 2015. Nigeria imposed tight movement restrictions in the restive northeast after Boko Haram bombings that killed more than 100 raised fears of fresh attacks over the Eid al-Adha festival. The military said the use of all vehicles would be banned throughout Borno state during the Muslim festival, which is known as Sallah in Nigeria and marked with two days' public holiday from Thursday. (Photo by Pius Utomi Ekpei/AFP Photo)

“Woman with Umbrella in Rain” by Raimund von Stillfried. Artist: Kusakabe Kimbei (Japanese, 1841–1934), 1870s. Commercial photography studios in Meiji-era Japan were renowned for the subtlety and refinement of their coloring techniques. This hand-tinted image of a young woman caught in a heavy rainstorm achieved its naturalistic effect by knitting together multiple strands of artifice: the greenery in the foreground was a studio prop; the flaps of the kimono were suspended by thin wires to create the impression of a strong wind; and long, diagonal marks were made on the negative to suggest streaks of rain. (Photo courtesy of The Metropolitan Museum of Art)