On the River Noord, just 23 kilometers east of Rotterdam, is the beautiful little village of Kinderdijk (the "children's dyke"). Taking its name from a famous legend that describes a baby's cradle being stranded here during the St. Elizabeth's Day flood of 1421, it's one of the most visited places in the Netherlands. Each of its 19 perfectly preserved 18th-century windmills is designated as a UNESCO World Heritage Site. Built between 1722 and 1761, together they comprise the largest surviving concentration of windmills in the country, a history that's celebrated during special Mill Days, when their sails are once again set in motion.