The Tien Son Grotto lies in Phong Nha – Ke Bang tourist complex that comprises natural beauty-spots in Quang Binh Province. The site is now on the list to be recommended to UNESCO for recognition as a World Heritage Site. Tien Son Grotto was discovered in April 1935 in the limestone mountain of Ke Bang. It is about 400m away from the famous Phong Nha Grotto and at a height of 135m. Tien Son Grotto is more than 980m long. Going into the cave for about 400m, visitors will see an abyss, about 10m deep. Then comes another part of the cave, about 500m long is rather dangerous for walking. At present, nearly 400m of the cave have been installed with lighting system to make it safe for visitors. Some look like a man or an animal, and there is one that looks like the Learning Tower of Pisa in Italy. On the cave ceiling, there are glittering gold and silver-like veins. Some stalagmites produce an echoing sound when slightly knocked. Limber Howard, Chief of the British Royal Team of Cave Researchers, who visited and made studies of the site, said that Tien Son Grotto may have been formed tens of millions of years ago. A river ran through the limestone mountain and eroded it. Then huge rocks fell, separated the mountain and form the cave. An under ground river ran through the lower part of the mountain, creating Phong Nha Grotto. Thus, Tien Son Grotto is older than Phong Nha Grotto and they do not link with each other. Geographical tectonics in Tien Son Grotto is rather stable.