A palatial ruin in Philadelphia built from the riches of an industrial golden age, linked by money and blood to the Titanic disaster. Hitler's headquarters in France, built to oversee the Nazi invasion of Britain but used to defend against the Allied reconquest of Europe. In Italy, an opulent island-stronghold converted to contain the country's mafia elite. And a country palace in Poland, the scene of a honey-trap devised to ensnare Napoleon.

Exploring a nuclear-armed facility in Arkansas that served as America's last line of defence in the Cold War and an industrial relic in Wales that felt a young Winston Churchill's wrath.