2.1K views · 20 reactions | London, Rome and Paris… Three cities, three stories, one mystery: their constructions. Known as the world’s best megastructures, these buildings hold secrets which, until now have been kept hidden from view. From covert Nazi resistance meetings deep in the underground tunnels of London, to understanding the secrets behind the construction of Christianity’s holiest of places. Secret Cities premieres tonight 7:30pm AEST. | HISTORY | Facebook