Mù Cang Chải's rice terraces climb the Hoàng Liên Sơn mountains in thousands of ribbon-thin steps, many just a metre or so wide. Every one was cut into the hillside by hand. There are no machines up here: each level holds water only because someone standing in the mud shaped and packed its earthen lip, and the whole staircase is fed by streams led down from the peaks. The Hmong have farmed these slopes for generations, following each curve of the land and stacking the fields up the valleys like a vast green amphitheatre. Some 2,200 hectares of terraces spread across the district, with the most celebrated gathered around the villages of La Pán Tẩn, Chế Cu Nha and Dế Xu Phình. Vietnam protects the terraces themselves as national heritage — the fields as a work, not the view.
The valley wears two completely different faces through the year. In late May and June, farmers flood the fields ahead of planting, and for a few weeks the terraces become thousands of mirrors, each step holding a piece of sky. By mid-September the ripening paddy washes the slopes in gold, and the harvest runs through October. Come early in the day and you will find mist sliding down the ridges, water buffalo working the mud, and Hmong women moving along the narrow dikes with seedlings bundled on their backs. The widest view is from Khau Phạ Pass — the horn of heaven, one of the four great mountain passes of the northwest — which often floats above a sea of cloud. In the golden weeks it becomes a launch point for paragliders drifting over the terraces below. Between those two windows the fields are plain green, and almost nobody comes.