the castle, the cathedral was built by Gundulph, Bishop of Rochester, in the 11th century (in 1080 to be precise). There has been a church on the site since King Ethelbert build a small cathedral for Bishop Justus in 604.
Although the cathedral isn't huge, it is very impressive and certainly warrants a visit.
The graveyard outside is mentioned in several of Dickens' novels, and is also the final resting place of several of the Dorrit family, presumably the inspiration behind Little Dorrit.
Inside the Cathedral
The pulpitum screen separates the quire from the rest of the cathedral. Eight Saints and Bishops with connections to Rochester are depicted on it.
To the left of the door to the quire are (from left to right):