Situated in the northeast region of Vietnam, Ha Long Bay is a part of the Gulf of Tonkin, and comprises the regions of Ha Long City , the township of Cam Pha and a part of the island district of Van Don. To the south-west it borders the island of Cat ba, to the cast is the sea and what remains borders the mainland with a coastline of 120km. Ha Long bay is made up of 1,969 islands of various sizes, 989 of which have been given names. There are two kinds, limestone and schist, which are concentrated in two main zones the south-east (belonging to Bai Tu Long Bay), and the south-west (belonging to Ha Long Bay). The densely concentrated zone of stone islands, grottoes and caves, world famous for its spectacular scenery, forms the central zone of Ha Long bay which has been named on of UNESCO's World heritage Sites. The bay itself has an area of 43,400ha, comprises 775 islands and forms a triangle: with the island of Dau Go (Driftwood Grotto) to the west; the lake of Ba Ham (Three Shelter Lake) to the south; and the island of Cong Tay to the east.