Storm surge barrier that is one of the largest moving structures in the world. The Maeslantkering is one of a series of surge barriers, locks, and dikes in the Netherlands, further described in the Delta Works article. The visitors center (het Keringhuis, €2 per person) explains the history of Maeslantkering as well as the wider context of Dutch water management, but exhibits are in Dutch only. Several times per day, guided tours are provided for €4 per person (most are in Dutch, some in English); check the website for time and reservations. It's also possible to get a good, free view of the barrier from the top of the dune next to the visitors center. Once a year (usually in September), the barrier is closed and re-opened for testing. On that day, the place will be relatively crowded.