At the south end of Centre Street, directly under New York City Hall, is the City Hall Loop and its abandoned station, which was the southern terminus of the original IRT subway line. Closed since 1945.
Times Square Subway- I stood in a pouring thunderstorm once before running into this quickly flooding train entrance in Times Square. Water off the streets was pouring down the side of the entrance like a waterfall. Once inside, I had to teach two NYC policemen how to purchase and use metro cards.