UK Castles....which ones are a must see?

[Scraptographer]

For those going to London and possibly spending extra time there, you may want to consider googling the 'Day's Out pass' or it may be called the '2for 1 days out pass' ? Essentially if you buy a London Underground (ie subway) ticket at a train station - not just at a subway station, you can use it to get 2 people in to some of the bigger sites for the price of 1! We used it for the Tower of London, Mme Tussauds, and the Churchill War Rooms, and there may have been others - I do believe that it can be used for some castles as well.