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 Rohingya refugee girl named Rufia Begum, aged 9, poses for a photograph as she wears thanaka paste at Balukhali camp in Cox's Bazaar, Bangladesh, March 31, 2018. (Photo by Clodagh Kilcoyne/Reuters)

Composite picture of lightning strikes over Colima, Mexico in just 5 minutes on July 14, 2020. These incredible photos show over 50 forks of lightning striking a city in just five minutes – in a storm being dubbed “The Night of a Thousand Forks”. The amazing, panoramic photos over the valley shows the whole sky light up as the forks of lightning strike at different points along the length of the city's 165 square miles. (Photo by South West News Service/Action Press)

“The Reward”. “A spot that a friend and I found that takes a bit of effort to get to. Needs the right swell and wind direction to come together for the backwash to really happen. We had been many times with OK results, but this morning everything lined up perfectly and I was rewarded with this split-second moment in time under some amazing morning light”. (Photo by Scott Harrison/2019 UK Surf Photo of the Year)

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)

Reuters South Africa-based photographer Juda Ngwenya who documented Nelson Mandela's historic rise to power died on Wednesday. Here: Prostitutes wait at a bar in a plush northern suburb of Johannesburg August 22, 2002. (Photo by Juda Ngwenya/Reuters)

A tourist struggles in the water, before standing up and wading away, after a wave strengthened by the influence of Typhoon Dujuan hit a river bank in Hangzhou, Zhejiang province September 29, 2015. (Photo by Reuters/China Daily)