Halong attracts around 90% of visitors coming to Vietam It's a Bay that 1,500 square km wide belonging to the TonkinGulf of the South China Sea. Ha Long, one of the World Heritages, it has nearly 2,000 islands and islets, all are limestone and dolomite, with numerous grottoes. Each one has its own characteristic with various caves: Sung Sot Cave, ThienCungCave, Trinh Nu Cave.