Watermills are structures that use the energy of flowing water to perform work, typically grinding grain into flour. They consist of a water wheel that turns when water flows over it, converting the kinetic energy of the water into mechanical energy. This energy can then be used to power various machines. Historically, watermills played a crucial role in agriculture and industry, especially during the Middle Ages. They were often built near rivers or streams to take advantage of the natural water flow. Today, while less common, some watermills are still in operation and serve as a reminder of early technological advancements.