Son doong cave is a cave in Phong Nha-Kẻ Bàng National Park, Bố Trạch district, Quảng Bình Province, Vietnam. Currently the biggest known cave in the world, the cave is located near the Laos-Vietnam border. Inside is a large, fast-flowing underground river.
In early August 2013, the first tourist group explored the cave on a guided tour at a cost of US$3,000 each. The group had six members from Australia, Norway, Russia and USA and spent 7 days and 6 nights for the tour. Next exploration trips will be arranged.

These amazing pieces of artwork from a series called “TaxCut” have been created entirely out of money. Chad Person an artist from California created these collages from hundreds of tiny pieces of American dollar bills. Photo: Kraken. (Photo by Chad Person/Caters News)

Festival goers plays in mud during the 15th Annual Boryeong Mud Festival at Daecheon beach in Boryeong, about 190 km (118 miles) southwest of Seoul, July 15, 2012. About 2 to 3 million domestic and international tourists visit the beach during the annual mud festival, according to the festival organisation. (Photo by Chung Sung-Jun)

A hen, a dog and a rabbit playing cards, circa 1956. (Photo by Evans/Three Lions)

A six-day-old hippopotamus is pictured next to his mother, Kara, aged 21, on September 12, 2012 at “Planet sauvage” (“Wild planet”) Zoo in Port-Saint-Pere, western France. The birth, a rare event for this species in captivity, occured on September 7, 2012 in the Zoo. (Photo by Frank Perry/AFP Photo)

The sun sets over the sea looking towards Lands End viewed from Gwenver beach near Sennen Cove on February 7, 2011 in Cornwall, England. (Photo by Matt Cardy/Getty Images)

In this March, 2015 photo, a person sits at an upright piano that had been hauled up to Topanga Lookout in the Santa Monica Mountains in Calabasas, Calif. For a couple of days last week, a Southern California hilltop was alive with the sound of mystery. Hikers venturing to Topanga Lookout found a battered upright piano sitting on a graffiti-scrawled concrete slab with a panoramic view over the mountains between Calabasas and the Pacific Ocean. Turns out, the piano was used for a music video by Seattle-based artist Rachel Wong. The cinematographer, Michael Flotron, says he and four others used a dolly and rope to haul the 350-pound instrument a mile up the trail on Tuesday. After the shoot, it was too dark to get the piano back down. Flotron says people seem happy to leave it there. But if necessary, he'll haul the piano back down. (Photo by Michael Flotron/AP Photo)

A model presents a creation from Andres Sarda's Fall/Winter 2017 collection during the Mercedes-Benz Fashion Week in Madrid, Spain February 18, 2017. (Photo by Javier Barbancho/Reuters)