NY doesn't have that much of that kind of underground city. There's a lot of underground passages and shopping areas, more in the vane of Montreal's, but nowhere near as extensive. There is also abandoned underground infrastructure, such as dead subway lines, which are rumoured to contain some nonsense called the Mole People. I think thats a load of hogwash, but I am also pretty sure that there are homeless living there.
Yeah... about as likely as the for miles around underground structures that are supposed to be here in the SLC area. From what I've read on what appear to be very reliable web sites, the US government, several Alien factions and the Mormon church have all colluded to hide the existence of these aliens in these underground caverns. Apparently there was even something of a war at one time between different alien races and the humans. It's amazing that such things can occur right under my feet. It does, however, explain the Apple Beer's (non-alcoholic) that keep missing from my refrigerator at home. I just thought it was one of my kids, now I know it's aliens!
Mulder and Scully would be proud!