Kate accessorised her look with a navy blue clutch, powder blue pumps and delicate pearl earrings.
The Duchess of Cambridge has previously worn the stunning midi-dress in the publicly released family photos to honour Prince Charles' 70th Birthday.
With a series of images posted on the Duke and Duchess of Cambridge's official Instagram page, Kensington Palace shared the story behind the nineteenth-century mansion that became the home of British codebreaking in World War II.
"Today The Duchess of Cambridge visited @bletchleyparkuk, the home of British codebreaking — which played a major role in secret intelligence gathering during the Second World War, producing secret information which had a direct and profound influence on the outcome of the war."
Kensington Palace continued: "The Duchess joined schoolchildren for an immersive workshop (using a real Enigma Machine used during the Second World War), which saw them take on the role of codebreakers in June 1944."