Re: Nobody is quite sure what it was originally built for.
Dunwich being something of a disappointment when I learned it wasn't the Lovecraft version. Used to have a mighty fine chip shop on the beach, but also an early example of global warming.
Dunwich doesn't really have anything to do with global warming, the erosion of Dunwich is what gives us Orford Ness, and is down to longshore drift, where the prevailing wind causes waves to strike the beach at an angle, dragging loose material down the beach and depositing it. Over a long period of time, this erodes the beach enough that it reaches the cliffs, and erodes them too causing a collapse. That material is then dragged down the beach as well. At one point, the River Alde came out at Aldeburgh, now it comes out ~12 miles away. Wikipedia has a nice map with points showing the lengthening of the spit over time.