Empty buildings and infrastructures are full of the echoes of real people and vanished lives, leaving many questions unanswered and mysteries unsolved. We explore the worlds strangest engineering projects that created empty silent cities. We ask why a ruined cold war air base has become a no-go area and how a tiny Japanese mining island become the most over-crowded place on the planet. We find out if the street layout of the Soviet Union's model city become a matter of life or death for its population. And how did Nazi Germany create a huge mind control facility at a holiday resort?

• Andrew Gough
• David Caldwell-Evans
• Fran Scott