Hạ Long Bay or Halong Bay (Vietnamese: Vịnh Hạ Long, IPA: [vînˀ hâːˀ lawŋm] ) 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 islets in various shapes and sizes. Hạ Long Bay is a center of a larger zone that 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.
Hạ Long Bay has an area of around 1,553 km2 (600 sq mi), including 1,960–2,000 islets, most of which are limestone. The core of the bay has an area of 334 km2 (129 sq mi) with a high density of 775 islets. The limestone in this bay has gone through 500 million years of formation in different conditions and environments. The evolution of the karst in this bay has taken 20 million years under the impact of the tropical wet climate. The geo-diversity of the environment in the area has created biodiversity, including a tropical evergreen biosystem and a seashore biosystem. Hạ Long Bay is home to 14 endemic floral species and 60 endemic faunal species.Historical research surveys have shown the presence of prehistoric human beings in this area tens of thousands years ago. The successive ancient cultures are the Soi Nhụ culture around 18,000–7,000 BC, the Cái Bèo culture 7,000–5,000 BC and the Hạ Long culture 5,000–3,500 years ago. Hạ Long Bay also marked some important events in Vietnamese history, with many artifacts found in Bài Thơ mountain, Đầu Gỗ cave, and Bãi Cháy.Nguyễn Trãi praised the beauty of Hạ Long Bay 500 years ago in his verse Lộ nhập Vân Đồn, in which he called it "a rock wonder in the sky". In 1962, the Ministry of Culture, Sports and Tourism of North Vietnam listed Hạ Long Bay in the National Relics and Landscapes publication. In 1994, the core zone of Hạ Long Bay was listed as a World Heritage Site under Criterion VII, and was listed for a second time under Criterion VIII.