A woman and her son hold firecrackers during Diwali, the Hindu festival of lights, in Mumbai, India, November 4, 2021. (Photo by Francis Mascarenhas/Reuters)

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 man washes his horse as a woman bathes her son at concrete water pens under a flyover in a slum area in Kolkata, India October 21, 2016. (Photo by Rupak De Chowdhuri/Reuters)

Jason Bregartner and his son Jason Jr., 2, sit in costume with J.D. Mirable at a bustop during the NYC Zombie Crawl in New York, October 18, 2015. (Photo by Shannon Stapleton/Reuters)

English actress Liz Hurley, 55, poses topless in the snow in a photo taken by her son in United Kingdom at the end of January 2021. Brit stripped to white bikini bottoms from her own swimwear range and draped herself in a coat. (Photo by Instagram/The Sun)

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

An Armatix employee holds a “smart gun” by the company at the Armatix headquarters in Munich May 14, 2014. The gun is implanted with an electronic chip that allows it to be fired only if the shooter is wearing a watch that communicates with it through a radio signal. If the gun is moved more than 10 inches (25 cm) from the watch, it will not fire. A Maryland gun shop owner has dropped his plan to be the first in the United States to sell the so-called “smart gun” after a backlash that included death threats. (Photo by Michael Dalder/Reuters)

Gas-masked men of the British Machine Gun Corps with a Vickers machine gun during the first battle of the Somme, 1916. (Photo by General Photographic Agency/Getty Images)