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 tourist struggles in the water, before standing up and wading away, after a wave strengthened by the influence of Typhoon Dujuan hit a river bank in Hangzhou, Zhejiang province September 29, 2015. (Photo by Reuters/China Daily)

A woman carries an inflatable float with the sahpe of a portion of pizza in a Barcelona, on July 18, 2020. Four million residents of Barcelona have been urged to stay at home as virus cases rise, while EU leaders were set to meet again in Brussels, seeking to rescue Europe's economy from the ravages of the pandemic. (Photo by Josep Lago/AFP Photo)

A Shariah law official whips a woman who is convicted of prostitution during a public caning outside a mosque in Banda Aceh, Indonesia, Friday, April 20, 2018. Indonesia's deeply conservative Aceh province on Friday caned several unmarried couples for showing affection in public and two women for prostitution before an enthusiastic audience of hundreds. The canings were possibly the last to be carried out before large crowds in Aceh after the province's governor announced earlier this month that the punishments would be moved indoors. (Photo by Heri Juanda/AP Photo)

A dog sits in a plastic basin filled with water in Taipei, Taiwan, 05 May 2018. Betel nut seller Mr Luo, the dog's owner, said he puts his dog Ah Dai (Stupid Guy) in the water-filled basin whenever the weather get hot. Luo has a dozen pairs of glasses for Ah Dai, so the dog wears different glasses every day and many tourists take photos of Ah Dai. (Photo by David Chang/EPA/EFE)

A Rohingya refugee girl named Rufia Begum, aged 9, poses for a photograph as she wears thanaka paste at Balukhali camp in Cox's Bazaar, Bangladesh, March 31, 2018. (Photo by Clodagh Kilcoyne/Reuters)

In this April 3, 2019, photo, horses from Nepal cavalry rest in a stable after morning practice for Ghode Jatra festival in Kathmandu, Nepal. The “Ghode Jatra” is an annual horse festival celebrated on the Nepal Cavalry grounds in Kathmandu, which marks the defeat of a Hindu demon. (Photo by Niranjan Shrestha/AP Photo)

A man walks on a slackline during the 7th edition of the European “Marmotte Highline Project” (MHP) festival in Lans-en-Vercors, near Grenoble, eastern France, on July 4, 2019. The event, during which the participants will be able to evolve on the various highlines located in the Regional Natural Park of Vercors, takes place until July 7, 2019. (Photo by Philippe Desmazes/AFP Photo)