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)

Fire fighters, emergency service vehicles and a helicopter in Moskovsky Prospekt at the entrance to Tekhnologichesky Institut station of the St Petersburg metro in the aftermath of an explosion which occurred in a train at 14:40 Moscow timeon April 3, 2017. (Photo by Peter Kovalev/TASS)

People wear clothing to protect them from the heat while riding along a street in Hanoi, Vietnam, 24 April 2019. North and central Vietnam was recently affected by extreme hot weather, with the highest temperatures reaching over 40 degrees Celcius, according to the National Centre for Hydro-meteorological Forecasting. (Photo by Luong Thai Linh/EPA/EFE)

A leg of a “diablito” frog (Oophaga sylvatica) is photographed in a laboratory at a laboratory in the zoo of Cali, Colombia, on July 19, 2019. Colombia is the second country with the largest number of amphibians in the world after Brazil. More than 40% of amphibian species worldwide are in danger of extinction. (Photo by Luis Robayo/AFP Photo)

Boston Bruins center Charlie Coyle (13) goes airborne as New York Islanders goaltender Semyon Varlamov (40) makes the save in a shootout during an NHL hockey game, Tuesday, December 13, 2022, in Boston. (Photo by Charles Krupa/AP Photo)

“Kirill Oreshkin of Moscow is crazy. Without the aid of equipment or safety gear, Oreshkin climbs buildings, statues, and whatever he can get his hands on to dizzying heights and then takes the most gorgeous selfies imaginable”. (Photo by Kirill Oreshkin)

A visitor tries a baccarat game at the Global Gaming Expo (G2E) Asia in Macau, China May 19, 2015. (Photo by Bobby Yip/Reuters)

A man pulls a cart with collapsed cardboard boxes past boutiques in the Sinchon district in Seoul, May 5, 2015. (Photo by Thomas Peter/Reuters)