Hi- this is concerning Halong Bay specifically not Ninh Binh and area
Skip Halong Bay and look for a company that offers Bay Tu Long.
To give you an idea on Halong day 500 cruises per day- of which 200 stay overnight (all together in an area designated by local autorities)
Bay Tu Long +/- 50 cruises per day and less than 10 stay overnight- it makes a world of a difference (I sailed Halong regularly since 1998 and every year became more disapointed as more boats spent the night) This year I took a group to Bay Tu Long - It is Halong Bay as it used to be 20 years ago.