Voluntary Xchange alerts readers to the underground complex that accompanies the air rights developments above Grand Central Terminal and the throat trackage. There's one urban legend that part of Franklin Roosevelt's armored train is still parked under the Waldorf-Astoria. There's also a backup power supply for the electric trains, that I got into in August 2001 along with an assemblage of O Scalers.
During World War II, this complex was protected by armed soldiers. There's nothing that secret any more, but I bet mine was one of the last groups to be shown around down there.