Grand Central Terminal on 42nd between Lex and Madison - Opened on Feburary 2, 1913, Manhattan's only surviving large station (Pennsylvania Station was razed in 1964), hosts 67 tracks on two levels (41 on the first floor, 26 below). Every time I walk in there, I still feel the same magical feeling I felt the first time I walked in as a young railfan in 1977... it was such an un-railfan-able location, but knowing so much railroading (including all the IRT subway lines) was happening just below the floors, I was just enthralled to be there.
A photo essay on the New York Central's water level route between New York & Chicago in the New York Central, Penn Central, Conrail and CSX/Amtrak eras