On the south-east side of Halong Bay, about 25 km from Bai Chay Wharf, Cong Do (Vietnamese : Cống Đỏ) is in Bai Tu Long Bay in the region which recognized as the World Heritage. It has an area of 23,363 sq. m, and its mountain reaches a peak of 172 m.
The island features many lagoons, which are the residence of numerous species of sea-life, such as shrimp, crab, fish, squid and aquatic plants. On the south-west side of the island, there is a wide coral reef displaying a myriad of colors.
Coral reef ecosystem is more than 700 m long and 300 m wide. It is preserved almost undamaged. In the future, there are plans for the development of a zone for scuba-diving. On the south-east side of the island, vestiges of the ancient commercial port of Van Ðon were discovered. This confirms beliefs that Cong Do Island once held an important position in terms of foreign trade.