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)

People dressed as characters from the computer game “World of Warcraft” walk across a field near the town of Kamyk nad Vltavou, Czech Republic, April 28, 2018. (Photo by David W. Cerny/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)

Yakutsk, with a population of around 270,000, holds its own title: that of the coldest city on Earth. Here: Frost-encrusted house in the city centre. (Photo by Amos Chapple/Courtesy Images/RFE/RL)

Storks casts shadows as they search for food on the dried-up Lake May in southwest Turkey on October 30, 2021. (Photo by Seyit Konyal/Solent News)

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)

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)

A man walks on a slackline during the 7th edition of the European “Marmotte Highline Project” (MHP) festival in Lans-en-Vercors, near Grenoble, eastern France, on July 4, 2019. The event, during which the participants will be able to evolve on the various highlines located in the Regional Natural Park of Vercors, takes place until July 7, 2019. (Photo by Philippe Desmazes/AFP Photo)