Philadelphia's relationship with the underground is as old as the city itself, dating back to when Quaker settlers resided in caves alongside the Delaware River more than three hundred years ago. The City of Brotherly Love later became a national and world leader in the delivery of water, gas, steam, and electricity during the industrial age. The construction of multiple subway lines within Center City took place during the early twentieth century. An intricate subsurface pedestrian concourse was also developed throughout the downtown area for the city's inhabitants. From Thirtieth Street Station and Reading Terminal to the Commuter Rail Tunnel and transit lines that were never built, Philadelphia's infrastructure history is buried under the earth as much as above. Join authors Harry Kyriakodis and Joel Spivak as they reveal the curious aspects of the Quaker City's underground experience.