Secret Bunkers

The oldest of these concrete fortifications hail from the time before World War I, when the brick-walled fortresses of the 19th century needed massive strengthening due to new armor-piercing ammunition. After the experiences of trench warfare in World War I, several European post-war governments opted for elaborate bunker systems along their borders as a supposedly impregnable line of defense. Once restricted areas, they are now either ruins or mementoes of, both, the hot and the Cold War. In two episodes, we trace the story and the architectural highlights of eight of these secret bunkers.