Quang Binh plans to launch experimental adventure tours of Son Doong Cave, which is considered the largest in the world, in early August this year. Movie on Son Doong cave to be broadcast in 60 countries The tours were suggested by Howard Limbert, an expert of the British Cave Research Association (BCRA). As scheduled, the trial tours will be held twice a month with the participation of a group of only 7 tourists and 15 local guides. After a trial time, the tours will operate officially from February to August every year. Son Doong cave was first discovered in Phong Nha-Ke Bang National Park by a local man named Ho Khanh in 1991. The cave was then made known publicly in 2009 by a group of British scientists from BCRA, led by Howard Limbert, following their surveying trip in Phong Nha-Ke Bang Park. Limbert said the cave is five times larger than the nearby Phong Nha cave, previously considered to be the largest in Vietnam. Son Doong cave has a length of at least 6.5 kilometres. It is estimated to be 200 metres in width and 150 metres in height. The largest chamber of the cave is judged to be 250 metres in height. Scientists have also discovered a great number of stalactites in astonishingly extraordinary shapes and also primitive forests in the cave.