Ha Long Bay, or Halong Bay, is a UNESCO World Heritage site and a popular travel destination in Quang Ninh Province, Vietnam. The name Ha Long means “descending dragon.” The bay is characterized by thousands of limestone karsts and islets of various shapes and sizes. Ha Long Bay is the center of a larger area that includes Bai Tu Long Bay to the northeast and Cat Ba Island to the southwest. These broader areas share similar geological, geographical, geomorphological, climatic, and cultural characteristics.

Mount Yen Tu is one of the highest peaks of the Dong Trieu Mountains in northeastern Vietnam, located in Uong Bi City, Quang Ninh Province. It is about 50 km from Ha Long City and 110 km from Hanoi.

Yen Tu Mountain is known as the seat of the Truc Lam Yen Tu Zen sect, associated with the prestige of King Tran Nhan Tong, the third king of the Tran dynasty. Becoming king of Dai Viet (the ancient name of Vietnam) at the age of 20, King Tran Nhan Tong led the army and people of Dai Viet to defeat the Mongol Yuan invaders twice, in 1285 and 1288. He played an important role in building the most glorious feudal dynasty of Vietnam. At the age of 35, King Tran Nhan Tong left the throne to Prince Tran Thuyen (King Tran Anh Tong) and lived his final years as a Buddhist monk. King Tran Nhan Tong became the first ancestor of Truc Lam Yen Tu Zen, the Zen sect that has had a great influence on the spiritual life of the Vietnamese for centuries. During his stay on Mount Yen Tu, he founded a vast system of temples and pagodas to lead a religious life.