Introduction
Most travellers spend a couple of nights on Cat Ba Island. It's not really worth the effort to get here if you stay for a shorter time.
It's easy to fill half a day or more just exploring the island on a motorbike (or bicycle if you're fit enough). If you're planning on doing any real trekking, you'll need to add another half day or more. And If you haven't already taken a Halong Bay cruise, that's another full day.