While its very unlikely that there are monsters in the NYC sewers like in the movie C.H.U.D., there are still some dangerous things down there.
https://en.wikipedia.org/wiki/C.H.U.D.#Plot
Entertainment and excrement, WTF?
The monster in the sewer theme has been around for quite a while.
https://en.wikipedia.org/wiki/It_(1986 novel)
