We actually saw St Michael's Mount (top right) on our Fat Hen foraging weekend in October.
And this time two of the locations are quite near us. Witley Common in Surrey (bottom left) is just a half hour away, and Nymans Garden in Sussex (bottom center) is just over an hour away. Nymans in particular seems well worth a visit: a 20th-century garden with a collection of rare plants, surrounding a 'romantic' house, all set in 275 acres of natural woodland.
Penrhyn Castle in Bangor (bottom right) is much further afield but features one of my favorite things: a fully restored Victorian kitchen. The bowl on the scullery worktop is labeled 'K' for kitchen, but perhaps that could also be 'K' for Kristina?