People are fascinated by tales of fabled lost cities. Yet below Scotland's capital, hidden for almost two centuries, there lies a metropolis whose very existence was forgotten until recently. For almost 200 years Edinburgh was surrounded by a giant defensive wall. Unable to expand its boundaries, it became the most densely populated city in Europe. The towering tenements of the Royal Mile were a direct result of this massive overpopulation and, when the city buildings couldn't get any higher, people were forced to construct new edifices over what was already there. An underground slum developed which existed for over 350 years. Trapped in poverty and crime, these subterranean dwellers lived in darkness and misery, ignored by chroniclers of the time. Edinburgh's population came to believe that the underground city, out of sight and out of mind since its abandonment in the mid-19th century, had never been there at all. This work chronicles Edinburgh's secret city: its history and structure; its inhabitants and the lives they led; the story of its rediscovery; the amazing tales, both ancient and modern, that made it legendary; the areas where it existed; and where to find the parts that remain.