The Oosterschelde storm surge barrier, a massive operable sea dam with an artificial island at its center.
When you're really interested in this Oosterscheldekering you can visit Neeltje Jans (http://www.neeltjejans.nl/). This is an attraction where you learn everything about water and the Delta Works Deltawerken.
Veerse Meer
This is a lake or inland lagoon that was closed off to the sea in 1961. See (http://en.wikipedia.org/w...)