The Maeslantkering is a huge storm surge barrier in the Nieuwe Waterweg, which is a waterway located in the Netherlands, close to Hoek van Holland. The barrier automatically closes when needed. It is part of the Dutch Delta Works and known to be one of largest moving structures on Earth. If you wan to know more about this wonder of engineering then visit the website of  Het Keringhuis. As usual, more images are posted in a web album.