At 900 years old, Windsor Castle is the largest occupied castle and oldest official royal residence in the world. Windsor Castle is much more than a castle; the grounds include several homes, a large church and the royal palace. Situated 20 miles west of London, it is also the weekend home of Queen Elizabeth II.

Windsor Castle is officially the largest inhabited castle in the UK and, indeed, the entire world. Covering approximately 13 acres (5.3 hectares), it has been a royal residence for over 900 years and serves as a primary home for the British Monarch. While Windsor is the largest by "continuous occupation" and sheer architectural scale, Dover Castle is often cited as the largest by "walled area," covering a massive footprint on the White Cliffs of Kent. In terms of ruins, Caerphilly Castle in Wales is the second-largest in Britain behind Windsor, famous for its elaborate water defenses and leaning tower. However, if you are looking for the "biggest" in terms of tourist footprint and royal history, Windsor remains the undisputed champion. In 2026, it remains a major tourist draw, and its size is so vast that it contains its own chapel (St. George's), a massive library, and enough rooms to house hundreds of staff members and guests.