In this November 2, 2017 photo, Mathew Fulkerson and his wife Leigh Ann pose at their Subterra Airbnb located in a former underground missile silo base near Eskridge, Kan. It was designed to house a nuclear warhead six decades ago – but now, this Cold War silo is the perfect spot for a mini break at just $133 a night. (Photo by Thad Allton/The Topeka Capital-Journal via 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 cosplayer poses for a photograph during the Comic Market 90 (Comiket) event in Tokyo Big Sight on August 12, 2016, Tokyo, Japan. Many manga and anime fans wearing cosplay lined up in the sun for the first day of Comiket. Comiket was established in 1975 and focuses on manga, anime, gaming and cosplay. Organizers expect more than 500,000 visitors to attend this year's summer event which runs for three days until August 14. (Photo by Aflo/Splash News)

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 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)

A camel is pictured in front of the Saturn tracking complex at the Russian-leased Baikonur cosmodrome in Kazakhstan on October 9, 2018. An astronaut and cosmonaut are due to travel to the ISS on October 11 aboard a Russian Soyuz MS-10 spacecraft from the Baikonur Cosmodrome in Kazakhstan. (Photo by Kirill Kudryavtsev/AFP Photo)

A toddler sits on the winner of the giant pumpkin category during the RHS (Royal Horticultural Society) London Harvest Festival Show at RHS Lindley Halls on October 6, 2015 in London, England. The traditional harvest themed show runs October 6-7 and showcases a wide range of late summer grown fruit and vegetables. (Photo by Ben Pruchnie/Getty Images)

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)