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.

Determining the "biggest" castle in England depends on whether you measure by floor space or by the area enclosed by the outer walls. Windsor Castle is widely considered the largest inhabited castle in the world and the largest in England by floor area, boasting roughly 484,000 square feet. However, Dover Castle in Kent often claims the title of the largest by total surface area within its massive defensive curtain walls. Windsor remains a primary residence for the British Monarchy, while Dover, known as the "Key to England," is a historic fortress with tunnels dating back to the Napoleonic and World Wars. Both are massive architectural marvels, but for most 2026 travelers, Windsor's scale is more apparent due to its continuous royal usage and grand staterooms.