Originally Posted by
themicah
The Rockefeller Center system is probably the biggest one that's open to the public. But parts of it have been closed off in recent years.
I was near Rokefeller Center today and decided to explore the underground passageways, From what I saw several years ago, most of that is still operational (they were doing construction and closed a lot of it off then.)
I was able to start with the USB building, entering on 52nd street between
6th (ave. of the Americas) and 7th avenues and staying completely underground exit on 48th street near 5th avenue.