A complex of stone building near Hadrian's Wall that were built to keep Northern hoards at bay! Also, a top secret military facility in the American Midwest, A series of vast structures in Lithuania and a collection of decaying locomotives in the heart of Ethiopia.

A now silent site that played a pivotal role in defending the United States throughout the 20th century. Plus, a sprawling facility in Taiwan, a crumbling Italian fortress and a ghostly Ukrainian mansion.