Around 17% of the land area of the Netherlands has been reclaimed from the sea or lakes. This was achived by building dams and windmills. The latter were used to pump the water (as well as to grind grain into flour and to saw wood).
In 1740s a system of 19 windmills was built in Kinderdijk in order to drain the polders. Today these windmills are one of the most popular tourist attractions in the Netherlands.
The system did not always work very well. From time to time the land was flooded. In 1927 a diesel pump station was built as a replacement for the windmills. During the World War II there was not enough fuel for the station and the mills came to rescue.
You can get to Kinderdijk by bus or by boat from Rotterdam.