William Gibson points to a Tokyo newspaper article about supposed secret tunnels under Tokyo: “AKIRA-inflected secret city beneath Tokyo; retired construction workers whispering about the diamond-cutter required to tunnel existing concrete, when the maps show nothing but soil should have been there…”
Gibson also notes “subway fantasy is a genre unto itself.” Hard not to be when there’s so much disused or abandoned infrastructure just out of sight, just around the corner. I used to be fascinated by the glimpses of old platforms or entire disused lines you could see in Boston on the Green and Red Lines. There are, as you might imagine, dozens of sites about the phenomenon, including this one on New York and this one on Boston. There’s a master list here.