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 woman jumps with balloons while she poses for a picture at a park in Kiev, Ukraine May 6, 2018. (Photo by Valentyn Ogirenko/Reuters)

A woman takes photos as Mount Agung volcano sends up another plume of smoke, seen from the Kubu subdistrict in Karangasem Regency on Indonesia's resort island of Bali on July 5, 2018. Mount Agung roared to life again on July 2, belching a plume of ash 2,000 metres (6,500 feet) high, as well as temporarily shuttering the airport and grounding hundreds of flights after erupting the week before. (Photo by Sonny Tumbelaka/AFP Photo)

A USGS geologist making observations of the fissure 8 lava channel at sunset is pictured in this July 3, 2018 fisheye lens handout photograph near the Kilauea volcano eruption in Hawaii, U.S. (Photo by USGS/Handout via Reuters)

'The Dutch charity organization Mensen in Nood (people in need) hits the streets with a remarkable campaign. People in need are posing with the typical attributes of consumer culture. The price of a designer handbag (€32) is compared with the price of a whole week of food (€4), The price a pint of beer (€4.50) with the price of 50 liter clean water (€1.50). The pictures were taken by Swedish fashion photographer Carl Stolz.' - Occupy Design UK

Women wearing face-kini masks lie on a beach to rest in Qingdao, Shandong province, China, June 3, 2015. A pale complexion is highly prized as delicate and feminine in China while dark skin suggests tanning caused by farming the fields or other lowly, outdoor work. (Photo by Reuters/Stringer)

Employees wear "No-Face" masks during working hours at a service company in Handan, Hebei Province of China. As a service company, staff must smile to customers every day. On “No-Face Day”, staff wore masks to hide their facial expressions and allow them to relax. No-Face is a character in the 2001 animated movie “Spirited Away”, a silent masked creature who has no facial expressions.

Ice covered leafs are pictured on a tree near Amstall in northern Austria, December 2, 2014. Freezing fog and rain covered parts of the region with ice, causing blocked roads due to fallen trees and closed schools for security reasons, local media report. (Photo by Heinz-Peter Bader/Reuters)