A walker has left a handprint on a snow- covered tree trunk on Grosser Feldberg mountain in the Taunus mountain range, Germany, 16 January 2017. (Photo by Frank Rumpenhorst/DPA)

A French riot police officer is surrounded by flames, during a demonstration against the controversial labour reforms of the French government in Paris on September 15, 2016. Opponents of France's controversial labour reforms took to the streets on September 15, 2016 for the 14th time in six months in a last-ditch bid to quash the measures that lost the Socialist government crucial support on the left. Scores of flights in and out of France were cancelled as air traffic controllers went on strike to try to force the government to repeal the changes that became law in July. (Photo by Thomas Samson/AFP Photo)

Son doong cave is a cave in Phong Nha-Kẻ Bàng National Park, Bố Trạch district, Quảng Bình Province, Vietnam. Currently the biggest known cave in the world, the cave is located near the Laos-Vietnam border. Inside is a large, fast-flowing underground river.
In early August 2013, the first tourist group explored the cave on a guided tour at a cost of US$3,000 each. The group had six members from Australia, Norway, Russia and USA and spent 7 days and 6 nights for the tour. Next exploration trips will be arranged.

A herdsman stands on the back of a grey bull during a ceremony of driving sheep from their winter habitat to their summer pasture in the puszta or Hungarian steppe of Hortobagy, 183 kms east of Budapest, Hungary, 23 April 2016. Sheep are traditionally driven to their summer pasture at around St. George's Day in the Hortobagy region, because livestock breeding people traditionally consider St. George's Day the beginning of spring. (Photo by Zsolt Czegledi/EPA)

This combination photo of images released by HBO shows Emilia Clarke portraying Daenerys Targaryen in “Game of Thrones”. The final season of the popular series premieres on April 14. (Photo by HBO via AP Photo)

Various kinds of pumpkins, out of some 400 on display grown this season, are seen on sale at Franzlbauer farm in Hintersdorf, Austria, October 27, 2015. (Photo by Heinz-Peter Bader/Reuters)

Reflected in an ornament, a reporter takes a photo of the White House Christmas Tree in the Blue Room during a media preview of the holiday decor at the White House in Washington, U.S., November 29, 2016. (Photo by Kevin Lamarque/Reuters)