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)

Gray whale feeding at the surface and showing it's baleen. (Photo by Christopher Swann/Biosphoto)

The winner of the Miss Tattoo Brazil 2014 contest, Bruna Barros, shows a tattoo that says 'My body, my rules' during Tattoo Week, the largest convention of art in the skin of Latin America, in Sao Paulo, Brazil, 14 July 2017. A tattooed woman beauty pageant, the new trends and techniques of the tattoo world, body piercing and the environment of the art of definitively painting the body, are all due to be addressed during the seventh edition of the “Tattoo Week Sao Paulo“. (Photo by Sebastiao Moreira/EPA)

Muslims pray at the top of Mount Al-Noor during their Umrah Mawlid al-Nabawi “Birthday of Prophet Mohammad” in the holy city of Mecca, Saudi Arabia January 16, 2016. Muslims believe Prophet Mohammad received the first words of the Koran through Gabriel, at the top of Mount Al-Noor in the holy city of Mecca. (Photo by Amr Abdallah Dalsh/Reuters)

Pilot Akmal Bin Abdul Kahar watches South Korea's Black Eagles aerobatics team perform a manoeuvre during an aerial display at the Singapore Airshow at Changi Exhibition Center February 18, 2016. (Photo by Edgar Su/Reuters)

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)

Boeing 747-400 of KLM in approach for the “Princess Juliana” airport, Netherlands Antilles Sint Maarten on July 2, 2002. (Photo by LUPOO/Ullstein Bild via Getty Images)

The bride in her room, prepared for a traditional Chechen wedding ceremony in Grozny, Chechnya, Russia on November 24, 2016. (Photo by Valery Sharifulin/TASS)