Introduction to the water cave: It is about 3 kilometers long and has been developed for 350 meters. The deepest water is 17 meters and the width is 3-15 meters. The stalactite in the cave has a strange shape. There is a huge stalactite connecting the top and bottom of the cave, like a sea. The Dragon King’s “sea-fixing needle” also surprisingly revealed the extremely rare national protected animal giant salamander in the underground Hanoi. Taking a boat tour from the underground river is like visiting the Dragon Palace, and the scenery along the way is breathtaking.