Željava Air Base, situated on the border between Croatia and Bosnia and Herzegovina under Plješevica Mountain, near the city of Bihać, Bosnia, was the largest underground airport and military air base in the former Yugoslavia, and one of the largest in Europe. (Photo by Thomas Windisch/Exclusivepix Media)

A handout picture provided by the press service of MORTON Group of Companies, show the balloon of Russian adventurer Fedor Konyukhov in the sky during his solo round-the-world balloon flight just after taking off from a spot near Northam, 96 kilometres north-east of Perth in Western Australia, 12 July 2016. Fedor Konyukhov took off from Northam on 12 July 2016 in attempt to beat the record of 13 days of American aviator Steve Fossett. (Photo by EPA/Morton Press Service)

Nora Muaid stands in Zawraa Park on December 2, 2011 in Baghdad, Iraq. The park's 180-foot tall Ferris wheel opened earlier this year and is the second largest in the Middle East. (Photo by Mario Tama/Getty Images)

U.S. Army soldiers from the 2-82 Field Artillery, 3rd Brigade, 1st Cavalry Division, wait to load onto their armored vehicles as they prepare to convoy to Kuwait from Camp Adder in Iraq on December 7, 2011 at Camp Adder, near Nasiriyah, Iraq. (Photo by Joe Raedle/Getty Images)

South Korean special warfare command soldiers participate in winter military training exercise on January 11, 2012 in Pyeongchang-gun, South Korea. The South Korean troops train in temperatures below -20 degrees celsius to defend the country against any possible attacks from North Korea. (Photo by Chung Sung-Jun/Getty Images)

An American flag flutters on a young tree stripped of bark after a massive tornado passed through the town killing at least 116 people May 24, 2011 in Joplin, Missouri. The tornado that ripped through the town of about 50,000 people May 22, is being called the deadliest single tornado in the U.S. in 60 years. (Photo by Julie Denesha/Getty Images)

Tourist Police sit in the shade on a road leading to the Coptic Cairo area on May 27, 2011 in Cairo, Egypt. Protests in January and February brought an end to 30 years of autocratic rule by President Hosni Mubarak who will now face trial. Food prices have doubled and youth unemployment stands at 30%. Tourism is yet to return to pre-uprising levels. (Photo by Peter Macdiarmid/Getty Images)