In major cities all around the world today, skyscrapers loom overhead, taxis honk their horns and street vendors peddle their wares. But below lays city upon city - each with its fascinating and unknown history. "CITIES OF THE UNDERWORLD" explores these layers, which are often hundreds of feet deep, to examine a city's ancient cisterns, dank dungeons, eerie tombs, clandestine hideouts, and even underground shipwrecks that have been lost for hundreds of years. How did (and do) engineers build layer upon layer up to today's city streets? "CITIES OF THE UNDERWORLD" reveals the technological marvels that allowed the construction of one city upon another - literally. (Source: History channel) Currently 8.2/10