Kinderdijk is situated in the Alblasserwaard polder at the confluence of the Lek and Noord rivers. To drain the polder – like much of the Netherlands, Kinderdijk lies below sea level – 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 have been a UNESCO World Heritage site since 1997.
Info source: Wikipedia