Kinderdijk is near Rotterdam in the Netherlands. It is a world heritage site with 19 well-preserved windmills (including one which almost burned down a few years ago). The mills drain water from the Alblasserwaard polders which lie below sea level - this is the Low Countries after all.
A couple of the windmills seen from the public path on the opposite bank.
For more information you should check out the Kinderdijk web site (opens in a new window). It even tells you how to get there.