Ha Long Bay cruises and day trips are the only sensible way to see this, because the landscape is offshore and there is nothing to do with it from land. Ha Long Bay is a UNESCO seascape of more than 1,600 limestone islands in the Gulf of Tonkin. Kayak into Luon Cave, walk the chambers of Sung Sot, and watch the light change from a cruise deck before the day boats arrive. It is about 3 to 3.5 hours from Hanoi by road, roughly 155 km. A day cruise is $120 per adult and the price is the whole package: the return limousine transfer between Hanoi and the harbour, an English-speaking guide, a welcome drink, a buffet lunch, entrance and sightseeing fees, kayaking or a sampan boat, and the onboard pool and jacuzzi. Overnight cruises are priced by cabin rather than by seat, from $180 for a balcony cabin on the Lan Ha Bay and Cat Ba route, $193 for an executive balcony and $214 to $250 for a suite. Children are charged by age band, so a family total is rarely twice the adult fare. The real decision is one day against one night, and it is not close. A day cruise gives you the landscape and gets you back to Hanoi the same evening, which suits a short trip or a fixed onward flight. A night on the water gives you the two hours that make the bay memorable, early morning and late afternoon, once the day boats have gone. Two days and one night is the minimum that includes sunrise; three days and two nights adds the quieter stretches and stops the schedule reading like a checklist. If the bay itself is the reason you came north, take the night.