Kinderdijk is in a polder at the confluence of the rivers Lek and Noord. To drain the polder, a system of 19 windmills was built around 1740. This group of mills is the largest concentration of old windmills in the Netherlands.
The windmills of Kinderdijk are one of the best known Dutch tourist sites. They were placed on the list of UNESCO list of World Heritage Sites in 1997. --Wikipedia