Cat Ba Island is the largest island in Halong Bay. Located off the coast of Hai Phong City, its beaches are great for sunbathing and swimming during the summer months. The best time to go to Cat Ba Island is during the summer, between April and November. Swimming, snorkelling, and diving are the most popular things to do on the island. Travellers can also enjoy a day of trekking, caving, and rock-climbing on Cat Ba Island. Cat Ba Island has become the adventure-tourism capital of Vietnam, and many of the activities advertised are nature-based. The national park is a good place for a nature trek among the mangroves and freshwater lakes and it’s a good launching point for tours of Ha Long Bay and kayaking trips.