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 Bosnian special forces soldier returns fire 06 April 1992 downtown Sarajevo as he and civilians come under fire from Serbian snipers. The Serb extremists were shooting from the roof of a hotel at a peace demonstration of some of 30,000 people as fighting between Bosnian and Serb fighters escalated in the capital of Bosnia- Hercegovina. (Photo by Mike Persson/AFP Photo)

A koala named Lisa from Pappinbarra recovers from burns at The Port Macquarie Koala Hospital on November 29, 2019 in Port Macquarie, Australia. Volunteers from the Koala Hospital have been working alongside National Parks and Wildlife Service crews searching for koalas following weeks of devastating bushfires across New South Wales and Queensland. Koalas rescued from fire grounds have been brought back to the hospital for treatment. An estimated million hectares of land has been burned by bushfire across Australia following catastrophic fire conditions in recent weeks, killing an estimated 1000 koalas along with other wildlife. (Photo by Nathan Edwards/Getty Images)

An Iranian girl walks at the Tochal ski resort, in north of Tehran, Iran on December 12, 2019. (Photo by Nazanin Tabatabaee/WANA via Reuters)

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)

A cyclist rides in al-Qudra desert in the Gulf emirate of Dubai, on June 8, 2020. (Photo by Giuseppe Cacace/AFP Photo)

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 plane flies past the moon in west London on Monday, January 17, 2022. The first full moon – the Wolf moon according to native north Americans – of 2022. (Photo by Victoria Jones/PA Images via Getty Images)