In Sanjiang County, Guangxi, the Dong minority built covered bridges that have stood for centuries without a single nail or screw holding their wooden frames together. The film centers on the Chengyang Wind and Rain Bridge, also known as the Yongji Bridge, tracing how carpenters used interlocking joints and cantilevered beams to span rivers and support pavilions and pagoda-like towers above the water. Footage moves through the bridge's covered walkways, showing villagers using the structure as a market, meeting place, and shelter from rain, much as it was designed to be. Craftsmen and engineers explain the joinery techniques passed down through generations, and the film sets these methods against the practical demands of the region's climate and terrain. It also places the bridges within Dong cultural life more broadly, showing how a functional piece of infrastructure became a communal gathering space. The result is a close look at a building tradition that solved structural problems long before modern fasteners existed.