Located on the northeast side of Halong Bay No Chuanzi Island, No Chuanzi Island is a circular stone island. The center is a green and calm sea lake with a cave leading to the sea outside the island. The hole is 60 meters long. At the time of high tide, the height of the hole is about 2.5 to 4 meters. The hole is bowed back. Visitors take a boat to enter during the visit, which takes 20 minutes. It is more interesting for people like me who have never seen it.