Windsor Castle, UK

Windsor Castle is the oldest and largest occupied castle in the world, continuously inhabited for over 11 centuries. This 13-acre fortress on a chalk hill above the Thames serves as the official residence of the British monarch. Its 1,000-year-old Round Tower and sprawling State Apartments offer visitors a living history unmatched by any other European castle. In fact, Windsor Castle's continuous occupation outperforms #6 Bran Castle, which was built in 1388 and has only been inhabited sporadically. With 1.5 million annual visitors, it remains one of the UK's top attractions, drawing crowds with its majestic architecture and royal legacy.