Event curators Harry Parr (L) and Sam Bompas (R) sit in paddle boats in the Truvia Voyage of Discovery installation on the roof of Selfridges department shop on July 21, 2011 in London, England. Selfridges is opening its roof to the public for only the second time since WW2 to host the installation, which includes a boating lake with dyed water and bar. (Photo by Matthew Lloyd/Getty Images)

High winds blow sand across the highway near the original north shore of Owens Lake, now miles from the nearest pool of water, on May 5, 2007 near Lone Pine, California. (Photo by David McNew/Getty Images)

A competitor scrambles in the mud under barbed wire during the Tough Guy Challenge 2009 at South Perton Farm on February 1, 2009 in Wolverhampton, England. The biannual event to raise cash for charity challenges thousands of international competitors to run through a gruelling set of 21 obstacles including water, fire and tunnels after a lengthy run at the start. (Photo by Christopher Furlong/Getty Images)

A brilliant sunset makes for a fun silhouette picture by jumping between sand bars at Shi Shi Beach on the Olympic Peninsula Friday July 17, 2015. (Photo by Bettina Hansen/The Seattle Times)

Ukrainian Air Force officers attend a graduation ceremony at the National University of Defence of Ukraine in Kiev, April 24, 2015. (Photo by Gleb Garanich/Reuters)

A competitor participates in the Tough Mudder challenge near Henley-on-Thames in southern England May 2, 2015. (Photo by Eddie Keogh/Reuters)

A participant smiles at the annual Christopher Street Day parade on Kurfuerstendamm in Berlin, Germany, June 27, 2015. (Photo by Fabrizio Bensch/Reuters)

Four-month-old fox cubs squaring up to each other in Walthamstow, England on August 7, 2015. (Photo by Greg Morgan/Barcroft Media)