Lan Ha Bay: UNESCO World Natural Heritage
In September 2023, UNESCO officially extended the Ha Long Bay World Heritage Site to include the Cat Ba Archipelago and Lan Ha Bay. This milestone recognized the region as having outstanding universal value for both its tropical karst geomorphology and its extraordinary marine biodiversity.
Fact sheet
Inscribed under UNESCO criteria (vii) for superlative natural beauty and (viii) for significant geological processes. Home to ancient marine archaeology and rare endemic species.
Geological evolution of the karst towers
The limestone towers of Lan Ha Bay began forming over 500 million years ago from thick layers of marine sediments. Over the past 20 million years, a combination of tropical rainfall, subterranean rivers, and repeated sea-level changes dissolved the limestone, creating deep sinkholes known as *fengcong* and isolated vertical towers known as *fenglin*.
As the sea invaded the low-lying karst valleys at the end of the last Ice Age (about 10,000 years ago), the towers became sea islands and the sinkholes became the silent marine lakes you paddle through today.
Complete guide to Cat Ba island: National Park, beaches, town & motorbike routes. Cat Ba Island Guide →
Questions people ask
Can visitors see the Cat Ba langur in Lan Ha Bay?
The Cat Ba langur is one of the world's 25 most endangered primates, with fewer than 90 individuals surviving. They live high on vertical karst cliffs. Lucky cruise passengers occasionally spot a troop foraging along cliff edges near Dark & Bright Cave in the early morning.