The Wash
The most famous thing that people remember about the Wash is that "King John lost his crown in the Wash".  This is because, according to reports from the time, King John travelled from Spalding in Lincolnshire to Bishop's Lynn, in Norfolk in the year 1216.  He became ill and decided to go back.  While he took the longer route through Wisbech, he sent his luggage, including his crown jewels, along the seashore and across the mouth of the Wellstream where the water was not deep. This route was only safe when the tide was low.  The horse-drawn wagons moved too slowly for the incoming tide, and many were lost. The whole area at the time was an extensive wetland known as The Fens, which was later drained. It is close to sea level.