An abandoned trolley system lies beneath Washington D.C., known as the Dupont Underground. Curiously enough, a portion of the tunnels are located under Connecticut Ave, where Comet Ping Pong resides.
Dupont Tunnels 4-chan Post: http://boards.4chan.org/pol/thread/100550239#p100558360
DuPont Underground Video: https://www.youtube.com/watch?v=MHMCXqNSQZg
Dupont Underground Forum: http://forum.skyscraperpage.com/showthread.php?t=202931
Photos of Dupont: http://www.urbanghostsmedia.com/2013/03/historic-streetcar-trolley-tunnels-dupont-circle-washington-dc/
Ex FBI Head Ted Gunderson Satanic McMartin Preschool Tunnels: https://www.youtube.com/watch?v=9YLpvKAR5fA
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