Kim Quy cave or “Golden Turtle” cave is located on Dam Nam islet, with a peak 187m above sea level. In front of the grotto is Dam Bac Islet and Soi Sim Islet is behind. The grotto is 100 m long and 5 to 10 m wide, running in a north-south direction. There are many stalactites and a water spring flowing all year round.

That cave is called Kim Quy by local people in Halong Bay. There is a legend told that: after returning the holy sword which had assisted King Lê Thái Tổ in the battle against Ming invaders from China, the Golden Turtle swam toward the Eastern Sea. Then, with the approval of the Sea King, Golden Turtle continued to fight against monsters in this marine area. The turtle became exhausted and died in a cave. Consequently, the cave was named after the Golden Turtle. The image of Golden Turtle turned to rock is still there as the evidence for the legend of the old god in Hoan Kiem lake