Castle Acre is a rare Norman settlement. It has a Castle, Bailey Gate and Priory. There is an English Heritage priory located here. The priory is one of the best preserved and dates back to 1090. It is one of the most complete that I have seen so far.
I am not usually one for audio guides but I really liked the one that they give out here. Also they have a monk activity for children.
I think you could spend a good half of a day here seeing the priory and castle, going around the village, and having lunch in the local pub. Or pack a picnic and eat amongst the priory ruins.
Not too much to organise and a nice place to get away for the day.