Hà Giang is Vietnam's northernmost province, a maze of grey limestone towers running to the Chinese border, and what people come for is one road through it. The loop is about 350 kilometres over three or four days, driving yourself or sitting behind a local easy rider, and the plateau gives up what it has in the order the road meets it. The passes come first. Then the stop everyone makes: Mã Pí Lèng, near 1,500 metres, where a short railed ledge runs out to a lookout. Below your boots the Tu Sản gorge falls some 800 metres to the Nho Quế, the deepest river canyon in the region. From a pier below the pass a wooden boat takes you into the narrowest slot of it, where the walls come straight out of jade-green water and shut the sun out above you. The stone began underwater, and fossils of that sea still turn up across the plateau.
Off the tarmac, footpaths link the H'mong hamlets on the ridges, where families plant maize in pockets of soil between the rocks and carry firewood up in baskets on their backs. Below the houses the rice terraces are steps only a few metres wide, each held by a low wall of earth and stone, green through summer and gold in the week before harvest. On a Sunday the road ends at a market, Đồng Văn or Mèo Vạc, filling with the villages of the plateau and their indigo cloth and rice wine. In March the peach and plum trees flower pink and white between the stone walls, and by late October the rocky fields turn pink again with buckwheat. The road under the bikes was cut by hand. Between 1959 and 1965 more than a thousand young volunteers from sixteen ethnic groups broke it out of the rock with picks and crowbars. The Mã Pí Lèng ledge alone took nearly two years, carved by people hanging on ropes off a cliff that gave them nothing to stand on. The state named it the Happiness Road.