Cat Ba is an island of approximately 140 sq.km in Ha Long Bay, Northern Vietnam. It is commonly used as an overnight hotel stop on inexpensive package tours to Ha Long Bay run by travel agents from Hanoi.

Cat Ba is the largest island in the Bay and approximately half of its area is covered by a National Park, which is home to the highly endangered Cat Ba Langur. This golden-headed langur is rarely seen, as fewer than 100 specimens are thought to survive in the wild, although it is the subject of a well-organised conservation programme. The Park covers both land and marine areas and has a high biodiversity, although it is at risk from too rapid an increase in tourism. Other mammals in the Park include civet cats and oriental giant squirrels.
                                                                                                       (kiwipedia)