In this episode we visit the fortresses that successfully guarded Cork Harbour in Ireland for more than 400 years. The subterranean passageways under the harbor forts contributed to the effectiveness of these impregnable naval defenses, and at one time became the largest prison anywhere in Britain.
We visit a mineral mine with a difference. In the tunnels of Stirling Hill Mine in New Jersey, a chance discovery transformed the mine’s future. At one time they were digging dull grey metal ores, but the invention of electricity revealed an extraordinary display of colors, not previously seen.
And we venture into the well preserved tunnels of a former submarine base in the frozen fjords of northern Norway. It is now in private hands, but the base could re-enter service with the Norwegian Navy if a military need were to arise.
