Hide in Lan Ha Bay’s heart is Cat Ba Island spanning 260 km² that comprise the Cat Ba Archipelago. Although being separated from the land and be covered the rugged coastline, Cat Ba Island still presents two main parts as wild forest and offshore with 17,040 hectares of land and 9,200 hectares of sea.

The wild forest has many different ecosystems: mangrove forests, limestone forests, and coral reefs.
There are a diverse fauna and flora system in the Cat Ba archipelago with 2,320 fauna and flora species. There are 60 extraordinarily rare species on the endangered Vietnamese Red List. The Cat Ba langur resident in the park is a critically endangered primate and only resides in Vietnam. Cat Ba National Park is also renowned because of the archeological research that revealed that maybe humans have lived in these islands for more than 6,000 years.

Offshore starts from the coastlines consisting of rugged, craggy, jungle rocky cliffs. There are some small, smooth sandy beaches and tiny villages with traditional customs. Far a bit is Cai Beo finishing Village includes more than 300 houses living mainly by fishing and fish farming.