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)

Gray whale feeding at the surface and showing it's baleen. (Photo by Christopher Swann/Biosphoto)

The winner of the Miss Tattoo Brazil 2014 contest, Bruna Barros, shows a tattoo that says 'My body, my rules' during Tattoo Week, the largest convention of art in the skin of Latin America, in Sao Paulo, Brazil, 14 July 2017. A tattooed woman beauty pageant, the new trends and techniques of the tattoo world, body piercing and the environment of the art of definitively painting the body, are all due to be addressed during the seventh edition of the “Tattoo Week Sao Paulo“. (Photo by Sebastiao Moreira/EPA)

Icelandic horses walk in their paddock at a stud farm in Wehrheim near Frankfurt, Germany, as the sun rises Tuesday, June 1, 2021. (Photo by Michael Probst/AP 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)

A cat sits in front of a retro car owned by retired mechanic Mikhail Krasinets at an open-air museum of Soviet-era vehicles in the village of Chernousovo, Tula region, Russia on September 27, 2018. In the remote village of Chernousovo, retired mechanic Mikhail Krasinets tends to more than 300 ramshackle, Soviet-era cars, remnants of a once vibrant auto industry that crumbled with the fall of the Soviet Union. (Photo by Maxim Shemetov/Reuters)

A Kenyan model Ajuma Nasanyana waits behind the scenes before the fashion show showcasing African fashion and culture during a gala marking the launch of a book called “African Twilight: The Vanishing Rituals and Ceremonies of the African Continent” at the African Heritage House in Nairobi, Kenya on March 3, 2019. (Photo by Baz Ratner/Reuters)

Students from Cambridge University in England make their way home along Trinity Lane after celebrating the end of the academic year at a May Ball in Trinity College on June 18, 2019. (Photo by Joe Giddens/PA Images via Getty Images)