The Cat Ba Islands

A small boat drifts on blue-green water. On every side, pillars of limestone rise out of the sea, dozens of them, even hundreds, some tall and some low, covered in green moss and tropical trees. Behind those cliffs, with luck, an animal is leaping from one rock face to the next. Only about 92 of its kind are left on Earth.

This is the Cát Bà langur. It is the reason people come to the Cát Bà Archipelago.

The archipelago is made up of 367 islands, large and small, scattered across the Gulf of Tonkin and belonging to the city of Hải Phòng. The largest is Cát Bà Island, which covers more than 262 square kilometers. Many people picture Cát Bà as one island, but it is a whole archipelago. It has forest, sea, and caves. It also has natural lakes hidden inside the limestone mountains, which the people there call "tùng áng".

Cát Bà holds two UNESCO titles, and it helps to keep them apart.

In December 2004, at an international meeting in Paris, UNESCO recognized Cát Bà as a World Biosphere Reserve. A biosphere reserve is a UNESCO-recognized area where nature is protected and the people living there keep working the land. The reserve covers 26,241 hectares. Of that, 17,040 hectares are land and 9,200 are sea. The title honors a wide variety of living places: tropical rainforest on limestone mountains, mangrove forest, coral reefs, seagrass meadows, karst caves, and the tùng áng lakes.

Then, in September 2023, UNESCO named Cát Bà again. On September 16, at the 45th session of the World Heritage Committee in Riyadh, Saudi Arabia, the committee extended the World Natural Heritage site of Ha Long Bay. It joined the Cát Bà Archipelago to the bay as one shared site, "Ha Long Bay, Cát Bà Archipelago".

This is Vietnam's first World Heritage site that crosses provincial lines. Quảng Ninh and Hải Phòng share a single heritage site. Not all of the archipelago belongs to it, only the part outlined in the 2023 nomination file.

Now to the langur.

The Cát Bà langur is a primate known to science as Trachypithecus poliocephalus. It lives only on these islands and nowhere else on Earth. Only about 92 are left.

In the 1960s, thousands of langurs climbed the cliffs of Cát Bà. Then hunting and the loss of their forest homes drove the numbers down sharply. In the early 2000s, only 50 to 60 were left. A conservation program run by the national park's management board and international organizations has brought the number back up to about 92.

The International Union for Conservation of Nature rates the Cát Bà langur as Critically Endangered. It also places the langur on its list of the 25 most endangered primates on the planet.

Close to Ha Long Bay lies another place of note, Lan Hạ Bay, on the side of Cát Bà that belongs to Hải Phòng. Its limestone karst is the same kind as in Ha Long Bay, but it has far fewer tourist boats, and the bay is quieter and more open.

Since July 1, 2025, Cát Hải has been a special zone, formed by merging 12 earlier units. It covers about 287 square kilometers and has more than 71,000 people. It is part of the city of Hải Phòng.

The two UNESCO titles are not about paperwork. They honor a beauty that is rare on Earth: a langur leaping between the cliffs, a kayak paddle parting the clear water of Lan Hạ Bay, and the afternoon sun sinking behind the far limestone pillars.