Halong Bay lies 100 miles east of Hanoi, in the Gulf of Tonkin. A UNESCO World Heritage site, the bay contains over 1,600 limestone islets and islands covered with junglelike vegetation. Most are uninhabited, owing to their sheer and precipitous faces. Some of the islands contain freshwater lakes; many contain caves, either above sea level or those notched out by marine processes. Together the limestone pillars, islets, and islands form an area of exceptional scenic beauty.