Vietnam’s Son Doong cave, the largest in the world, could hold a 40-story skyscraper inside. The pristine ecosystem has its own river and jungle. Despite its size, Son Doong wasn’t discovered until 1991. It was lost again for nearly two decades and was fully explored for the first time in 2009. (Photo by Jason Speth/HuffPost)

A B-52 bomber is watched by a group of curious onlookers as it lands at RAF Fairford, February 21, 1999. The B52s arrived from the U.S.A. as part of NATO's preparations for air attacks on Yugoslavia as tensions in the Kosovo crisis increased. (Photo by Dylan Martinez/Reuters)

A woman looks at the honour guard soldiers marching at the Tomb of the Unknown Soldier by the Kremlin wall, in downtown Moscow, on June 28, 2021. (Photo by Alexander Nemenov/AFP Photo)

Britain's Catherine, Duchess of Cambridge, shelters from the rain under an umbrella as she arrives at the London School of Economics to mark the launch of The Royal Foundation Centre for Early Childhood, where she took part in a roundtable discussion on the Centre's inaugural report, “Big Change Starts Small” which was released today, in London on June 18, 2021. (Photo by Richard Pohle/Pool via AFP Photo)

Members of the “Exit Point” amateur rope-jumping group jump from a 44-metre high (144-ft) waterpipe bridge in the Siberian Taiga area outside Krasnoyarsk, September 13, 2015. Rope-jumping, an extreme sport, involves jumping from a high point using an advanced leverage system combining mountaineering and rope safety equipment. (Photo by Ilya Naymushin/Reuters)

Models pose in designs from May Quant's collection on a street in London, England, on October 16, 1969. Grania, left, wears the "Shimmy Shimmy," a white rayon dress over matching pants with a shawl. Baba, center, wears "Razzamatazz," a jumpsuit featuring plastic sequins in blue, silver and red on nylon. Linda wears "Muffit," a pink minidress with an old English style floppy mobcap. (Photo by AP Photo)

Morenada dancers perform during the “Senor del Gran Poder” (Lord of Great Power) parade in La Paz, May 21, 2016. (Photo by David Mercado/Reuters)

Elizabeth Nicolaou, a final year student with the Royal Academy of Dance, strikes a pose on April 28, 2022 near the Cutty Sark ship in Greenwich, London ahead of International Dance Day. First celebrated in 1982, International Dance Day has taken place every year since in anniversary celebration of the birth of Jean-Georges Noverre (1727-1810), considered the creator of modern ballet. (Photo by Guy Corbishley/Alamy Live News)