Many of Britain's most iconic historical sights stand supreme in the open for all to see: Hadrian's Wall, Stonehenge, St Paul's Cathedral and the country's abundance of castles for instance. Yet beneath our cities and towns too, stunning structures and buildings of the past have been painstakingly excavated by passionate volunteers trying to preserve their local history. No more so is this true than in Liverpool. The Second World War was hard on Liverpool. Its strategic position meant it became the terminus for 1/3 of all the imports into Britain during the Second World War. This made the city a big target for the German Luftwaffe and, outside of London, more bombs fell on Liverpool than any other city. Because of this it became too dangerous to keep key military command posts above ground. So they burrowed underground.They created a bunker complex which became the nucleus for British operations in the Atlantic during the war. There was where the Battle of the Atlantic was fought and won. It is not just World War Two history buried beneath Liverpool's streets. Beneath the once-palatial house of early-nineteenth century industrialist Joseph Williamson is an extensive labyrinth of beautifully-created tunnels. Only recently-excavated by a group of passionate volunteers, the extent and purpose of the tunnels is still a mystery. In this episode Dan visits these two extraordinary underground structures to find out more about Liverpool's hidden history.