Ha Long Bay is located in the Gulf of Tonkin and includes some 1,600 islands and islets, forming a spectacular seascape of limestone pillars. Because of their precipitous nature, most of the islands are uninhabited and unaffected by a human presence.
As the most extensive and best known example of marine-invaded tower karst in the world, Ha Long Bay is one of the world’s most important areas of Fengcong (clusters of conical peaks) and Fenglin (isolated tower features) karst. Abundant lakes, occupying drowned dolines, are one of the distinctive features of the Fencong karst, with some appearing to be tidal. Possessing a tremendous diversity of caves and other landforms derived from the unusual geomorphologic process of marine invaded tower karst, the caves are of three main types: remnants of phreatic caves; old karstic foot caves and marine notch caves.