Most international tourists do the bus from Hanoi to cruise and back to Hanoi. Which is a shame as Ha Long city itself is a nice town with several attractions in itself
One of which is the Bao Tang Quang Ninh (the Museum of Quang Ninh). While the focus is on the local area, many of the exhibits talk of Vietnam and the importance of Quang Ninh to VIetnam history and culture.
Some say all the exhibits are labelled in English but the expansive Geology, Zoology and Marine areas are not. Which is a shame as the geology, fauna and flora are definitely strong reasons why many visitors come here in the first place. I also found the marine and botanical sections a little dated with many of the exhibits faded to a ubiquitous white (or brown for the botanicals).
But they have really done a good job overall, with many different sections covering the history, archeology, musical, artistic, industrial and warfare contribution this extremely rich province has made to Vietnamese history.
The top floor is given over to the coal mining industry and initially this might seems strange. However, not far to the north of Ha Long is Bai Tu, the site of the largest coal seam in Vietnam. It is ironic that the same geology that produced the natural wonder of the Ha Long - Bai Tu coast line has also given us the huge mineral deposits that are now, due to illegal and disastrous mining practices pouring millions of liters of polluted water into that self same bay.
The museum is modern, airconditioned, wheel chair friendly. I did two visits - one at 8 am on a Thursday morning where I had the whole place to myself! Utterly fantastic. I visited again the following Sunday and while the hoards of vistors were a distraction, it was a tour guide who insisted on using an amplifier to pontificate to her small group of Vietnamese and whose voice could be heard clearly from all three floors. Hardly what you would expect in a museum where one is bent on studing and appreciating culture. The idiot guide made it seem more like a market
As others have mentioned, the nearby shoreline is also scenic, with several of the iconic karst pinnacles within meters of the wide, well paved walk way. Several hundred meters further on is the huge, mushroom like Expo center that looks like an alien spaceship. Free entry but it does not always open at the posted times
Well worth a visit!