Kim Quy Grotto or Golden Tortoise Grotto is situated on Dam Nam Islet, with a peak 187m above sea level. The front is Dam Bac Islet and Soi Sim Island behind.
The grotto is 100m long and 5 to 10m wide, running in a north-south direction. A narrow way leads to the interior of the grotto where a stream flows. The stalactites here are snow-white and lightly hang from the ceiling.
And in the compartment, Bach Dang wood pile battlefield appears with more than 30 piles which were used by Tran Hung Dao King to plug in Bach Dang river still remain here, the dark brown cracked wood seem to be fallen, yet they are extremely strong. That they are stalagmites, they are distributed everywhere, denser, but there are ways clearly, highly polished and about 30 – 40cm, looks like real wood pile yard.
It is linked to the ancient legend of the Golden Tortoise: after having helped Emperor Le Loi defeat his enemies, the Golden Tortoise took back the magic sword he had given him, and swam towards the sea. Arriving in Halong Bay, it met with so many evil spirits and demons hindering its journey that it remained to do battle. After having defeated them all, the Golden Tortoise was so exhausted that it searched for a grotto to rest in, and once inside, turned to stone.
Today in the grotto, it can be found dozing, still with ancient wounds covering its body.