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 last known individual of the subspecies was a male named Lonesome George (Spanish: El Solitario Jorge/George), who died on 24 June 2012. In his last years, he was known as the rarest creature in the world. George served as a potent symbol for conservation efforts in the Galápagos and internationally”. – Wikipedia. (Photo by Rodrigo Buendia/AFP)

Elephants munch on Christmas trees in their enclosure at Berlin's Zoologischer Garten Zoo on January 4, 2013 in Berlin, Germany. Traditionally, the animals get in the first week of the year leftover Christmas trees. (Photo by Andreas Rentz)

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)

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.