Visit to Windsor Castle, the vacation home of the British Royals - Aug. 2017. Windsor is in the English county of Berkshire. It is notable for its long association with the English and later British royal family and for its architecture. The original castle was built in the 11th century after the Norman invasion of England by William the Conqueror. Since the time of Henry I, it has been used by the reigning monarch and is the longest-occupied palace in Europe. Inside the castle walls is the 15th-century St George's Chapel