National Windmill Day, also known as Nationale Molendag, is celebrated on the second Saturday and Sunday in May, particularly in the Netherlands. This event invites people to explore the history and significance of windmills, which have been utilized for centuries to harness wind energy for various purposes. On this day, approximately 950 windmills and watermills open their doors to the public, allowing visitors to learn about their inner workings and the role they play in sustainable energy. Celebrations often include community events and educational activities, encouraging people to appreciate the beauty and functionality of these structures. In addition to visiting windmills, individuals are encouraged to read about their history and advancements, as modern wind turbines are a rapidly growing source of renewable energy.