Hạ Long Bay scatters roughly 1,600 limestone islands across the Gulf of Tonkin, the drowned remains of a karst landscape that took some 500 million years to form. When the sea rose and flooded the old limestone plateau, only its steepest pinnacles stayed above water, leaving the forest of sheer towers that gives the bay its shape today. Its name means "descending dragon": an old legend tells of a mother dragon and her children, sent by the Jade Emperor, who spat pearls and jade into the sea to wall off invaders — jewels that are said to have hardened into these islands. Inscribed as a UNESCO World Heritage Site in 1994 and later named one of the New7Wonders of Nature, the bay hides caves, still lagoons, and a handful of floating fishing villages among its channels.
The way to see it is from the water. Traditional wooden junks thread the narrow straits between the towers, slipping past coves that open only from the sea. You can climb into Sung Sot, the "Surprise" cave and the largest in the bay, where lit chambers of stalactites open one after another deep inside an island, then paddle a kayak under low sea arches into lagoons walled off by rock and utterly still. The signature way to take it all in is to stay a night aboard: as the sun drops between the peaks the water turns to copper, and at dawn a low mist snags on the island tops and blurs them into pale silhouettes. The bay is heavily travelled — hundreds of cruise boats work the main routes — so many now steer south to the quieter Lan Ha Bay for the same seascape with fewer hulls around them.