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 man poses for a picture in front of Christmas lights decoration at the Francisco Morazan square in San Salvador, El Salvador, December 22, 2020. (Photo by Jose Cabezas/Reuters)

In this photograph taken on July 7, 2018, an Indian Buddhist monk plays with the wind amongst prayer flags on a hill overlooking Tnagyud Gompa monastery in Komik in Spiti Valley in the northern state of Himachal Pradesh. (Photo by Xavier Galiana/AFP Photo)

Tibetan pilgrims walk outside the Sera Monastery in Lhasa, Tibet Autonomous Region, China, 11 September 2016. Sera Monastery is known as one of the “great three” Gelug university monasteries of Tibet founded in 1419. (Photo by How Hwee Young/EPA)

A girl plays on a pile of discarded flowers outside a market, the day after the Diwali celebrations in Mumbai, India October 31, 2016. (Photo by Shailesh Andrade/Reuters)

A resident gestures about the loss of his home following an overnight fire at the Addition Hills area in suburban Mandaluyong city east Manila, Philippines, Monday, November 14, 2016. Fire officials say the overnight fire destroyed hundreds of homes, rendered more than 5,000 people homeless and resulted in the death of two residents. (Photo by Bullit Marquez/AP Photo)

“These Rajasthani sisters were sitting on the staircase inside their house relaxing and enjoy a cup of masala chai”. (Photo by Firdaus Hadzri/National Geographic Travel Photographer of the Year Contest)

Drivers push cars to gas station during “oil crisis”, Roslindale, Boston, Massachusetts, 1973. (Photo by Spencer Grant/Getty Images)