You can't actually go inside it - it's derelict. In the 1930's, the Earl of Lonsdale ran up huge debts and could no longer afford the upkeep of the castle, so he essentially abandoned it. It was then sequestered by the army during WW2 and used as a weapons research base and the gardens were used for tank training.
It's got no roof and it's full of 6ft high plant life. The only part you can enter is tea rooms and the gift shop.
