Tuan Chau island or Sentinel Chau Island is 3 km west of Dau Go cave. The island is approximately 3 km2. This island is inhabited by people. The nurturing hands of humans have turned this island into a fertile farm producing vegetables and fruits for the outlying mining and fishing villages of Ha Long Bay.
According to the inhabitants, Tuan Chau is a derivative of two words. Before the revolutionary war, each island was under the surveillance of an officer. Each was in charge of a group of sentinels assigned to keep security for one island in the bay. There were several of such officers assigned to Ha Long. The Vietnamese words, linh tuan means sentinel(s) and tri Chau means mandarin (officer) Chau, hence the combination of the two words means Tuan Chau or Sentinel Chau.
There is a bamboo hut on the island that has became a shrine, since it was rumored that this place was favored by Ho Chi Minh when he visited Ha Long. The hut is maintained and kept by the people of the island. Today visitors to the island can visit the hut as if it was a historical monument.
Poem Mountain stands over the city of Hon Gai. On his visit to Ha Long, King Le Thanh Tong (15th century) wrote a poem glorifying Ha Long's beauty. This poem is carved on a stele on Nui Truyen Dang which was later renamed Nui Bai Tho or Poem Mountain. The King was a poet and the person responsible for forming the group of intellectuals, Tao Dan Nhi Thap Bat Tu, or Tao Dan twenty-eight scholars.
Cua Ong Temple is located on a hill over looking Bai Tu Long Bay. The temple was built as a shrine to mandarin Tran Quoc Tang, the son of Vietnams most famous general Tran Hung Dao.
In 1283, during the height of the war against Mongolia, Tran Quoc Tang was sent here to build a fort to defend this frontier. This area was known for its rough and less than ideal conditions. Tran Quoc Tang created a government here and turned the area into a prosperous place. Tran Quoc Tang was made supreme commander and became one of Vietnams most successful general. During this period, there were many bands of outlaws and pirates harassing the people in this region. General Tang successfully wiped out many of these bandits and brought peace to this area. He was also successful in keeping the great Mongolian army at bay during their numerous attempt to invade Vietnam. The people revered him so much that he became a demigod to them. So much reverence was given to general Tang that he was dubbed King of the Sea while he was still alive!
General Tang died in 1313 at the age of 61. The people in the region mourned his passing and built a shrine in his honor. Today, the words Great Eastern Sea King are still imprinted on the placard at the entrance of the temple. Den Cua Ong was built in the Le dynasty (17th century), but was later remodeled in the Nguyen dynasty (17th - 19th century). Every year during Tet, Vietnamese new year, the people in this area have a festival to celebrate and honor General Tang.