Colchester castle is definitely worth a visit if you are interested in history and visiting the area – worth paying a little extra for the tour experience as you will real,y learn a lot about the history of Colchester

Built on the foundations of the Roman Temple of Claudius, Colchester Castle is the largest Norman keep in Europe.
Now a museum, it showcases the history of Colchester from Celtic Kings, through Roman invasion and Boudiccan revolt, to Norman conquest and medieval life.
Its Civil War story and terrible link to Witchfinder General, Matthew Hopkins can also be explored in the surviving prisons.

http://www.colchestercastlepark.co.uk/colchester-castle/