There are several ways to reach Halong Bay from Hanoi:
1. Day Trip: Day trip packages are available for most countries embarking in Hanoi to Halong Bay. Very general, however, is for transportation to and from the bay, at least by bus or minivan, a cruise around that bay, and some lunch on board. From Hanoi it usually takes about 3-4 hours in both directions, thus making for an extended day, but an excellent option for short-time visitors.
2. Overnight Cruise: Overnight cruising will let you soak into the glamour of the Bay; you could kayak, explore caves, or savor the sunset. Cruises vary from budget, single-deck boats, up to luxury cruising yachts. Most of the cruises pick you from your hotel and transport you to Halong Bay.
3. Private Transfer and Tour: Take a private car and a driver to Halong Bay; if you would like a way to go with a more customized experience, in this way, your time would be flexible, and you would stop by a few noteworthy places on the way. Thereafter, you will join in a cruise or hire a private boat into Halong Bay.
4. Seaplane: Flying from Hanoi to Halong Bay in a seaplane permits a special taste of travel. Quite a bit more expensive, sea plane flights offer aerial views of the bay and other landscapes around it. The flight lasts for about 45 minutes and can be combined with a cruise or day trip.
In general, you should aim to be visiting Halong Bay during the dry season, which runs from October up to April, should the weather appeal.