Pennsylvania Castle is a Gothic Revival clifftop mansion on the Isle of Portland, Dorset, rather than a medieval fortress, and is now a private estate and event venue overlooking Church Ope Cove.
Architecturally a late 18th‑century Gothic Revival country house, built of Portland stone with crenellated parapets, so it reads “castle” in silhouette rather than in function.
it was Built 1797–1800 for John Penn, Governor of Portland and grandson of William Penn, the founder of the American colony of Pennsylvania, which gives the house its name.
 
Interesting facts...
Thomas Hardy fictionalised the house as “Sylvania Castle” in his novel The Well‑Beloved.
It is believed Churchill, Eisenhower and De Gaulle once sat around a table in the drawing room at Pennsylvania Castle to discuss or plan aspects of the D‑Day landings.