Long-tailed mayflies (Palingenia longicauda) at Tisza river near Tiszainoka 135km (84 miles) southeast of Budapest, June 23, 2013. Millions of these short-lived mayflies engage in a frantic rush to mate and reproduce before they perish in just a few hours during “Tiszaviragzas” or Tisza blooming season from late spring to early summer every year. (Photo by Laszlo Balogh/Reuters)

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.

Rene Penia drives his VW Beetle 1995, locally called “Vocho”, through the streets of Monterrey April 22, 2015. The car was painted by a local artist to be part of an exhibition on the 1960s at the National History Museum in Monterrey where it was on display for five years. Pena bought the car for 25.000 Mexican Pesos (some USD 2,000 at that time) in 2013 during an auction and he then converted the car into an electrical vehicle. (Photo by Daniel Becerril/Reuters)

Vincent Yu is a multiple award winner who won Honorable Mention in the 2013 Photographer of the Year category for Pictures of the Year International. Photo: A statue of Hotei Buddha sits in the debris in the tsunami-destroyed town of Sendai, Miyagi Prefecture, northern Japan Friday, April 1, 2011. (Photo by Vincent Yu/AP Photo)

In 2013, the United Nations General Assembly officially designated November 19 as World Toilet Day, which is coordinated by UN-Water in collaboration with governments and partners. Here: An open-air toilet and a hot spring shower are seen in the middle of nowhere on the road to the Krafla geothermal power station and lava fields, near Reykjahlid and Lake Myvatn in northeastern Iceland, on August 19, 2012. (Photo by Mariana Suarez/AFP Photo)

A local miner wades through water as he walks down from a mountain in Benguet a day after Typhoon Haima struck northern Philippines, October 21, 2016. Super Typhoon Haima slammed into the northeastern Philippine coast late Wednesday with ferocious winds and rain that rekindled fears and memories from the catastrophe wrought by Typhoon Haiyan in 2013. (Photo by Erik De Castro/Reuters)

In this photo taken Sunday, May 6, 2012, Denis Lutskevich, left, is detained by police during an opposition rally in Bolotnaya Square in Moscow. The former naval cadet and first-year student, 21-year-old Lutskevich was attending his first protest when he was detained, and is still in prison Monday May 6, 2013, on the first year anniversary of the protest. (Photo by Pavel Golovkin/AP Photo)

Members of the Castellers “Vila de Gracia” start forming their famous human tower called “castell” in the Barcelona neighborhood of Gracia, Catalonia, Spain on Sunday May 19 2013. A “castell” is a human tower traditionally built during festivals in many places in Catalonia. At these festivals, several "colles" or teams compete to build the most impressive towers they can. (Photo by Emilio Morenatti/Associated Press)