that's so cool!! DO ENJOY! it'll be lots and lots of fun!! take tooons of pictures, maybe buy an extra memory card?
well i was only there for a short time and one castle i did enjoy was Warick Castle if you're going about there. it has lots of different activities planned throughout the day and its just really well organized.
Cardiff Castle was oky, not as cool as Warick I think. but hte interior of the castle was quite impressive.
those were the only two touristy places i was able to go.