In the Scottish capital of Edinburgh, hidden from view, a series of vaults tell a murky story of opportunity, crime and destitution; at Fort Schwatka Unalaska are the remains of an Alaskan battleground, where a foreign invader set foot on American soil for the first time since 1812; The Old Herring Factory is a remote Icelandic facility that played a major role in transforming the nation's economy; and in the calm waters of Croatia's Adriatic Sea, Fort Punta is a vast fortress charts the rise and fall of a European empire.