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)

The Aurora Borealis (Northern Lights) is seen over the sky near the village of Pallas (Muonio region) of Lapland, Finland September 8, 2017. (Photo by Alexander Kuznetsov/Reuters)

Visitors gather outside Ark Encounter, a 100 million USD, 510-foot-long re-creation of Noah's Ark in Williamstown Kentucky, USA, 05 July 2016. Ark Encounter is the brainchild of Australian-born creationist Ken Ham; it was built with the help of state tax incentives and the sale of 62 million USD in junk bonds. (Photo by Jim Lo Scalzo/EPA)

The Blue Man Group performs on stage during a media preview ahead of their show in Singapore on March 31, 2016. Blue Man Group was started by three friends in New York in 1991 as a way to celebrate the human spirit through music, science, art and theater. (Photo by Roslan Rahman/AFP Photo)

Riot police stand guard behind a fire as refinery workers hold a blockade of the oil depot of Douchy-Les-Mines to protest against the government's proposed labour reforms, on May 25, 2016. Refinery workers stepped up strikes that threaten to paralyse France weeks ahead of the Euro 2016 tournament as the government moved to break their blockades, escalating a three-month tug-of-war over labour reforms. (Photo by François L.O./AFP Photo)

Boeing 747-400 of KLM in approach for the “Princess Juliana” airport, Netherlands Antilles Sint Maarten on July 2, 2002. (Photo by LUPOO/Ullstein Bild via Getty Images)

Migratory flamingos arriving from Europe are seen in Port Fouad Nature Reserve, on the outskirts of Port Said Governorate, Egypt on December 12, 2022. (Photo by Mohamed Abd El Ghany/Reuters)

Ellesse Janda welcomes a spring rainbow at Cresswell in Northumberland, United Kingdom on March 17, 2023. (Photo by Ian Sproat/Picture Exclusive)