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 Bosnian special forces soldier returns fire 06 April 1992 downtown Sarajevo as he and civilians come under fire from Serbian snipers. The Serb extremists were shooting from the roof of a hotel at a peace demonstration of some of 30,000 people as fighting between Bosnian and Serb fighters escalated in the capital of Bosnia- Hercegovina. (Photo by Mike Persson/AFP Photo)

An elephant “kisses” a visitor during a show at an elephant training school in Xishuangbanna, Yunnan province, April 18, 2015. Some 16 elephants live at the school and give four 30-minute performances everyday for visitors. (Photo by Wong Campion/Reuters)

Migrants climb through the windows of a train bound for Serbia at the train station in Gevgelija, The Former Yugoslav Republic of Macedonia, 19 July 2015. Thousands of migrants who crossed Greece are on their way through Macedonia towards Serbia in order to access other European countries. Hungary in mid-July started to put up a fence on its border with Serbia, which makes the situation with the migrants in the transit countries even more complicated. The European countries on 20 July will discuss the quota of how many migrants each country should accept. (Photo by Georgi Licovski/EPA)

A Palestinian youth demonstrates his parkour skills on a street in Gaza City, January 15, 2016. (Photo by Suhaib Salem/Reuters)

This picture taken on January 26, 2016 shows a monkey sitting on a bench during rehearsal at a monkey training school in a zoo in Dongying, eastern China's Shandong province. Shows featuring performing simians, popular in China and throughout Asia, are expecting a boost in the Lunar New Year of the monkey, which begins on February 8. But they are facing a growing backlash from Chinese people concerned about animal welfare. (Photo by Wang Zhao/AFP Photo)

Hindu devotees laugh as they watch the religious festival of Lathmar Holi, where women beat the men with sticks, in the town of Barsana in the Uttar Pradesh region of India, March 17, 2016. During Lathmar Holi the women of Barsana beat the men from Nandgaon, the hometown of Krishna, with wooden sticks in response to their teasing. (Photo by Cathal McNaughton/Reuters)

In his series of untitled photographs Nobody Claps Anymore, the Mexican-American photographer Alec Dawson portrays ordinary people in their homes in a downbeat, ultra-stylised manner. Staring into space as they watch TV or water the garden, the real-life subjects of photographer hint at vast reserves of boredom and regret. (Photo by Alec Dawson)