Dao Gu Cave or Cave of Wonders is located on Dao Gu Island in the southwest of Halong Bay, and it is the largest cave in the Gulf region, and when it was first discovered by French tourists in the nineteenth century, they called it "the Cave of Wonders" because of its large areas. Spacious and amazing landscapes, and the cave inside contains three large rooms, each of which includes majestic scenes of stalactites and stalagmites and historical writings dating back to the voyages of the French, and because of its large open entrance, the cave is characterized by a damp atmosphere, and in the third room there is a large fresh water lake.