If the ectoplasm is connected to the secret tunnel accessed from the city then I have absolutely no clue how to access that either. I'm under the assumption that it has something to do with the guy standing outside the the shop that goes slightly transparent when you get close to him, but I can't seem to interact with him at all. Actually, I tried again to see if I could figure out how to interact with him and found out that the Ivan's pants also go slightly transparent, so I'm not sure if the transparency is a bug or if that's supposed to happen.