Rice fields at Sapa, Lào Cai, Vietnam (© Anujak Jaimook/Getty Images)

Long before these terraces became famous, they were built for a simple purpose: growing rice. In Vietnam, generations of farmers gradually shaped Sapa's mountain slopes into productive fields. In Lào Cai province, these stepped terraces have supported local communities for centuries. Built and maintained by ethnic groups such as the Hmong, Dao, Giáy and Tày, the terraces are designed to hold rainwater as it flows downhill. This makes rice farming possible where flat land is scarce. The design also helps to reduce soil erosion and conserve water.