We are not well blessed with Castles in Suffolk although there are sites known where between 20-30 once existed, there are stumps and stubs in some places and then there is the Curtsain Walled Framlingham Castle
Wingfield Castle dates back from 1384 originally as manor house, this castle has its own moat and drawbridge
As far as I know we only have one fort in Suffolk and that is Landguard, in Felixstowe. Here the last attempted invasion of England took place when hundreds of the Dutch Military attempted to take the fort, they were repelled. For two hundred years Landguard Fort and the Redoubt [and a previous building] im Harwich guarded the entrance to The Stour Estuary
I have a photo somewhere of Little Wenham Castle reputed to be Suffolk's oldest inhabited brick building, until I find just the top of the tower I hope this link will suffice