Ever since that day in the garden of Eden when Adam and Eve tried to escape the gaze of God, humans have been devising new ways to hide. From the chilling secret headquarters of the Nazis to the secluded gentlemen's clubs of London, from the chapel of the Holy Grail in Spain to the private banks of Switzerland, the world is filled with closed doors where people hide their precious goods, their sacred objects or even themselves. 

Authors Stephen Klimczuk and Gerald Warner have unearthed some of these hiding places in a fascinating book called Secret Places, Hidden Sanctuaries: Uncovering Mysterious Sights, Symbols and Societies. Gerald Warner joined us to share a few secrets.