Ha Long means descending dragon, and the legend says a dragon family came down from heaven to spit out jewels that became the islands, which is as good an explanation as any for nearly two thousand limestone towers rising from green water. UNESCO listed the bay in the 1990s for its scenery and its geology, and the Cát Bà archipelago to the south joins the same landscape of steep karst islands, hidden lagoons and floating fishing villages. The scale is hard to describe: islands shaped like teeth, like ships, like sleeping animals, all standing in a calm, jade-coloured sea.
Cát Bà Island, the largest in the group, is also a biosphere reserve, with forest, mangroves and caves, and it is home to the Cát Bà langur, one of the rarest primates on earth, which you are most unlikely to see. The local economy runs on tourism and fishing, and the bay is busy with tour boats, so do not expect solitude, but you can often find calm if you go early or in the shoulder seasons. The ride here is a different kind of adventure from the mountain passes: you are on the edge of the sea, and the road is a way to see it.
Roads around Hạ Long are good by Vietnamese standards, with a coastal road past the Bãi Cháy waterfront and over a long bridge, and heavy traffic in the town. The approach from Hanoi is by expressway, which is fast but monotonous, and the real riding pleasure comes when you leave it for the smaller roads. Tourist season brings congestion, especially at weekends, and the weather matters: typhoons can arrive between June and October, and sea mist in late winter can reduce views to nothing. October to April is generally the better window.
Hạ Long has fuel, restaurants and hotels in abundance, with fresh seafood served along the front, including grilled squid and a local fish cake called chả mực. Boat trips to the islands depart from the harbours, and the ferry to Cát Bà leaves from nearby ports, so check schedules and whether you can take a motorcycle aboard. Book ahead in high season, since the bay is very popular, and carry sun cream and a light waterproof.