Dover Castle, famously known as the "Key to England," is a massive medieval fortress that has stood as a guardian of the nation's coastline for over 2,000 years. Built on a site that includes a Roman lighthouse and an Anglo-Saxon church, the castle was heavily fortified by Henry II in the 12th century, featuring the imposing Great Tower. Throughout its history, it has played a vital role in national defense, from the Napoleonic Wars to World War II, when its secret wartime tunnels served as the command center for the evacuation of Dunkirk. It remains a colossal social and historical landmark, offering visitors an immersive look at England's defensive evolution through the ages.