This castle was built to strengthen the defences at the closest point to the European mainland. The spectacular Constable's Tower dates from the early 13C. Beneath the castle, the Secret Wartime Tunnels, a maze of tunnels and secret chambers dating back to Napoleonic times, were used as a command post during Operation Dynamo in 1940. The guided tour, accompanied by sound effects and other installations, at times somewhat macabre, lend the site an almost Orwellian atmosphere.