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)

An Iranian girl walks at the Tochal ski resort, in north of Tehran, Iran on December 12, 2019. (Photo by Nazanin Tabatabaee/WANA via Reuters)

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 Ainu (アイヌ?), also called Aynu, Aino (アイノ), and in historical texts Ezo (蝦夷), are indigenous people or groups in Japan and Russia. Historically they spoke the Ainu language and related varieties and lived in Hokkaidō, the Kuril Islands, and much of Sakhalin. Most of those who identify themselves as Ainu still live in this same region, though the exact number of living Ainu is unknown. This is due to ethnic issues in Japan resulting in those with Ainu backgrounds hiding their identities and confusion over mixed heritages. In Japan, because of intermarriage over many years with Japanese, the concept of a 'pure Ainu' ethnic group is no longer feasible. Official estimates of the population are of around 25,000, while the unofficial number is upwards of 200,000 people”. – Wkipedia

Photo: A captive bear drinking from a large bottle held by an Ainu tribeswoman. (Photo by Evans/Three Lions/Getty Images). Circa 1955

Rick Sorenson, owner of the Rio Ramaza Marina, wades in the Sacramento River after securing an old paddlewheel boat on his property as the river makes its way up the levee on Garden Highway in Sacramento, Calif., Monday, January 9, 2017. (Photo by Hector Amezcua/The Sacramento Bee via AP Photo)

Snow falls as a woman walks her dog in the village of Podolye, 70 kilometers (43 miles) east of St. Petersburg, Russia, early Thursday, May 11, 2017. North winds brought snow to the east of the St. Petersburg region. (Photo by Dmitri Lovetsky/AP Photo)