下龍灣
The karst landscape of Hạ Long Bay is of international significance and of fundamental importance to the science of geomorphology. The fenglin tower karst, which is the type present in much of Ha Long Bay, is the most extreme form of limestone landscape development. If these karst landscapes are broadly compared in terms of their height, steepness and number of their limestone towers, Ha Long Bay is probably second in the entire world only to Yangshou, in China. However, Hạ Long Bay has also been invaded by the sea so that the geomorphology of its limestone islands are, at least in part, the consequence of marine erosion. The marine invasion distinguishes Ha Long Bay and makes it unique in the world. There are other areas of submerged karst towers which were invaded by the sea, but none is as extensive as Ha Long Bay.