What medieval castle had the most impressive defence? Murud-Janjira in India. Designed to protect the coast, it has never fallen to attack from invaders including efforts by the Dutch, Portuguese, and even the British.

While many castles boast impressive walls, the Tower of London in the United Kingdom is often cited as the most "continuously protected" castle in the world. For nearly 1,000 years, it has served as a royal palace, a prison, an armory, and the home of the Crown Jewels. Its protection is multi-layered: it features massive concentric walls, a moat (now dry), and is guarded by the Yeoman Warders (Beefeaters), who are all retired high-ranking military veterans. Additionally, because it houses the Crown Jewels, it has an incredibly sophisticated electronic security system and a dedicated unit of the Royal Guard (soldiers in red tunics and bearskin hats) who patrol the grounds with modern firearms. Another contender is the Potala Palace in Tibet, which is physically protected by its massive 5-meter-thick stone walls and its position 3,700 meters above sea level. In terms of modern security, the Imperial Palace in Tokyo is also highly protected by the Imperial Guard and restricted access zones. However, for a blend of ancient stone fortifications and elite modern military protection, the Tower of London remains the gold standard of high-security historical landmarks.