I visited Halong Bay on a 2 day tour from Hanoi. It is a beautiful area of limestone islands off the northern Vietnamese coast. The only disappointment is the lack of birdlife that should occur around these islands.
From Cat Ba Island
The group trip I took went to the coast in a large bus and we had lunch at a seaside restuarant. Then we boarded a ferry for a three or four hour cruise to Cat Ba Island. We had dinner and spent the night in a nice hotel there, and in the morning took another cruise back to the mainland and ate at same seaside restuarant before journeying back to Hanoi.
From ferry boat
Aboard the ferry boat watching the scenary unfold. It was a very beautiful and relaxing trip. I got to meet and talk with some of the members of the group while basking in the sun, although somewhat overcast the two days both days, on the top deck.
What's really great:
Visiting a limestone cave on one of the islands was very interesting. Trinh Nu cave was was well developed for mass tourism with concrete walkways and area lights, no crawling or spelunking about with a headlight.
The scenery from the bus to and from Halong Bay
I was on a tour so I did not have a choice of accomodations on Cat Ba, but the hotel I stayed in was very nice (Sorry do not remember the name.). There are quite a few hotels and restuarants here most catering to group tours from Hanoi.
Ferries docked at Trinh Nu
There are numerous open air bars in Cat Ba. I had a few Bia Hoi here, which is the Vietnamese tap beer served for about 15 cents a glass. The glass size and the brand of beer varies from place to place. There also seem to be numerous prostitutes and massage parlors as this is a port and tourist town.