At weekends, Cat Ba, the largest of the islands in Halong Bay, is transformed into a lively coastal resort, which can be explored by motorbike or bicycle. Following the creation of a national park, around half of this unspoilt karstic formation, which has a few sandy beaches to the northeast of the port of Cat Ba, benefits from protected status. Walk up the slippery footpath to the top of the island for a view of the surrounding bay and the strange vegetation that carpets its limestone peaks.