Ha Long Bay is a sea of limestone. More than a thousand karst towers and islets rise straight out of the Gulf of Tonkin, their cliffs hung with jungle and hollowed into caves. Ha Long means descending dragon, after a legend of a dragon that scattered jewels across the water to hold back invaders. At first light, with mist sitting between the peaks, the story seems perfectly reasonable.
The bay is a UNESCO World Heritage Site and one of Vietnam's most visited places, so how you see it matters. A day trip covers the highlights in a rush. An overnight cruise lets you kayak into quiet lagoons, watch the light change on the rock at sunset and wake to water that is almost still.