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 Palestinian female masked militant from the Al-Quds Brigades, the military wing of the Islamic Jihad, takes part in an Islamic Jihad rally in Rafah, southern Gaza Strip, 29 July 2016. (Photo by Mohammed Saber/EPA)

Musicians in Father Frost costumes ride along Nevsky Avenue on the Dedmorobus (portmanteau of “Father Frost” and “bus”) musical bus to entertain citizens ahead of New Year celebrations in St Petersburg, Russia on December 28, 2020. (Photo by Alexander Demianchuk/TASS)

A Saudi police officer receives emergency calls at a call center, ahead of the Hajj pilgrimage in the Muslim holy city of Mecca, Saudi Arabia, Tuesday, August 6, 2019. The hajj occurs once a year during the Islamic lunar month of Dhul-Hijja, the 12th and final month of the Islamic calendar year. (Photo by Amr Nabil/AP Photo)

Father Christmas reading with three young children. (Photo by Spencer Arnold/Getty Images). Circa 1915

Father Christmas hands out presents to children at the Aid And Adoption Society home at Leytonstone. (Photo by Gerry Cranham/Fox Photos/Getty Images). 7th December 1938

A man and his son ride a horse at Tahrir Square in Sanaa, Yemen on January 21, 2021. (Photo by Khaled Abdullah/Reuters)

This Monday, September 15, 2014 photo shows glazed bricks displayed at the Iraqi National Museum in Baghdad. The Islamic State militants seek to purge society of all influences that don't conform with their strict, puritanical version of Islam. That means destroying not only relics seen as pagan but also Muslim sites they see as contradicting their ideology, particularly Sunni Muslim shrines they see as idolatrous as well as mosques used by Shiites, a branch of Islam they consider heretical. (Photo by Hadi Mizban/AP Photo)