National Mills Day is observed in the Netherlands on every second Saturday of May. This cultural observance celebrates the country's rich heritage of wind- and watermills, which are integral to the Dutch landscape and played a significant role in its economic development. On this day, approximately a thousand mills open their doors to the public, allowing visitors to explore these historical structures, many of which are run by volunteers. Mills are often decorated with flags and flowers, and while there is no entrance fee, donations are appreciated. The event coincides with National Cycling Day, making it an ideal occasion for a mill bike tour. Notable locations include the eight mills in and around Amsterdam, which highlight the enduring presence of these iconic structures in Dutch culture.