If you’re going to Ha Long Bay stay on Cat Ba island. We stayed at Cat Ba Hostel which was only $2 a night! It was in a nice location away from the noise but I don’t think there is any bad location on Cat Ba island. The two main places people go out at night is The Good Bar and The Rose Bar. Both you can play free pool. The Good Bar also has really good food.
One day we went on the boat trip that cost $19. They take you all around Lan Ha Bay and Monkey island. You get to kayak in the coolest looking caves and the last spot we were able to go snorkeling.
One day we rented motorbikes and went to Cat Ba national park where we went on a hike to the top of the mountain.
There is a really pretty beach walking distance from the main area.