Halong Bay is the one destination in Vietnam. There is definitely no words to describe the scenery. I head straight to Cat Ba island from Ninh Binh which is a 12-hour journey combining buses and ferry.
Driving a motorbike through Cat Ba island is an amazing opportunity to explore the area. The national park is by far the best sightseeing I have seen in Vietnam. Its hiking is a whole experience. You won’t see much until you reach the very top. Once at the top, you’ll be stunned by a breathtaking 360 view of Cat Ba island.
As you will probably stay for a couple of days there, I would recommend you to go for a day trip on a boat. You will be sailing through Ha Lam bay which is way less touristic than the real Halong Bay. They usualy drop you by some fish farms and insane coves including kayaking, swimming and other activities.