Son Doong is a recently discovered cave in Vietnam which is believed to be the largest in the world. The entrance to the cave, Son Doong, meaning cave of the mountain river was first discovered in 1991 by a local logger, Ho Khanh. A team of scientists and explorers contacted him in 2009 and requested his help to find the cave. It took months but he retraced his way back through the jungle. The scientists were shocked by what they saw.The cave is estimated to be about two and five million years old and is the largest cave passage in the world. It is more than three miles long with a number of chambers that are large enough to hold an entire city block of New York skyscrapers. It contains a number of formations including a 200 foot, Hand of the Dog which could be the worlds largest stalagmite and baseball-sized cave pearls which are much smaller. It is distinguished by two large dolines which are areas where the cave roof collapsed. This lets in light and created conditions for the prehistoric flora to grow in the middle of the cave. The cave runs for about 9 km and contains the tallest known stalagmites in the world which are about 70 mt tall.