A general view of Hong Kong's business district is seen Thursday, August 1, 2013. (Photo by Vincent Yu/AP Photo)

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 high temperature alerts were issued as a record-setting summer heat wave continued to bake most parts of south China. (Reuters)

A worker polishes an Oscar statuette at R.S. Owens & Company during a media demonstration February 9, 2012 in Chicago, Illinois. (Photo by Scott Olson/Getty Images)

Meatball, a bulldog, poses in a tuxedo at the Tompkins Square Halloween Dog Parade on October 20, 2012 in New York City. Hundreds of dog owners festooned their pets for the annual event, the largest of its kind in the United States. (Photo by John Moore)

New parents Chrissy Teigen and John Legend are seen leaving Khloe Kardashian's 32nd birthday party held at Dave and Buster's in Hollywood, California on June 28, 2016. (Photo by Splash News)

Rachel Hollon of Los Angeles was body painted as Harley Quinn at Comic-Con International in San Diego, USA on Jule 20, 2017. (Photo by K.C. Alfred/San Diego Union-Tribune via ZUMA Press/Rex Features/Shutterstock)

Operations & Exercises, 1st place. An RAF Voyager aircraft sits in the harsh winter weather at Mount Pleasant Complex, Falkland Islands, while personnel work to ensure the snow is cleared. (Photo by Sgt Andy Holmes/2020 RAF Photo Competition)