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Yelp
One of the largest, best preserved and most lavishly decorated keeps in England, surrounded by 20 acres of mighty earthworks. Begun in 1138 by William d'Albini for his new wife, the widow of Henry I, in the 14th century it became the luxurious exile-place of Queen Isabella.
So much for the history of the place; the castle is relatively small and you can look round it easily in under an hour.
It's great for kids and whilst you are in Castle Rising itself (a tiny, but pretty village), there is a gorgeous tea room and a pub to pop into.
If you are in the area, it is certainly worth a detour, but probably not worth making a long journey for.