Hạ Long Bay or Halong Bay is a UNESCO World Heritage Site and popular travel destination in Quảng Ninh Province, Vietnam. The name Hạ Long means “descending dragon”. Administratively, the bay belongs to Hạ Long city, Cẩm Phả city, and is a part of Vân Đồn District. The bay features thousands of limestone karsts and isles in various shapes and sizes. Ha Long Bay is a center of a larger zone which includes Bai Tu Long Bay to the northeast, and Cát Bà Island to the southwest. These larger zones share a similar geological, geographical, geomorphological, climate, and cultural characters.

The bay consists of a dense cluster of some 1,600 limestone monolithic islands each topped with thick jungle vegetation, rising spectacularly from the ocean. Several of the islands are hollow, with enormous caves. Hang Dau Go  is the largest grotto in the Ha Long area. French tourists visited in the late 19th century, and named the cave Grotte des Merveilles. Its three large chambers contain large numerous stalactites and stalagmites  There are two bigger islands, Tuần Châu and Cát Bà, that have permanent inhabitants, as well as tourist facilities including hotels and beaches. There are a number of beautiful beaches on the smaller islands.