Catherine is eager to see a "real" castle- that's why she's so hot to go to Blaise. The joke here is that Blaise isn't a really an old castle- it's an eighteenth century folly, on a rocky site, done up in appropriately gothic style. The whole effect was "enhanced" by Repton, who rearranged a bit of the grounds in the very early nineteenth century, and added nine houses for estate workers in the "cottage orné" style, and made the castle "ruin" habitable for the gamekeeper! I suspect that these bits had mot been built for Catherine to see, however, if we take the date of NA to be 1798...

1. A brief History of Blaise Castle, with views of Repton's designs, the manor house, etc.

2. A really good walk around the Blaise Castle estate, with lots of pictures, giving a great impression of what Catherine and co would have seen.