There is a great presentation on building the Grand Central Terminal on C Span-History. Barry Lewis, architectural historian does a great job explaining the building of the terminal and some of the history of NYC. Very interesting. The MTA control people work in the very top of the terminal but of course you can't visit that area. Also, did you know that the tracks actually turn under the roads/buildings so the trains can face north when they leave? It is not a stub end terminal. Also there is a 'station' under the Waldorf Astoria hotel that Pres. Roosevelt used to use. It is nothing fancy but a small platform. Also all the buildings above the underground train yard of course have no basements! It was built the same time that the Pennsylvania station was being built. It is worth a watch!
To pennsydave:
The control room can be seen by the public but only on a Metro-North guided tour.
I have been in the control room twice but there is also a visitor's room behind and above the control room that has a picture window for viewing the operation of the control room.
The loop tracks that you mentioned that are on both track levels are no longer in use
because all the trains are either mu electrics or push-pull locomotive operated trains that have a control cab car at the opposite end from the locomotive.
The station you mentioned under the Waldorf Astoria is just one low level platform that was used by President Roosevelt once. The box car that carried his limo is still stored there. I have been there and stood along side it. It has doors at each end for unloading and loading his limo and an elevator was built in the building to carry his lomo up in the building.
If you have a chance to visit Manhattan this May, Metro-North is having a festival of trains on May 11th and 12th at the terminal. They plan to have dozens of vintage passenger cars that operated in and out of the terminal in the past on long distance trains from 1913 thru the 1960s there open for inspection. In addition they will also will have locomotives and cars from their current roster.
I own a dvd from National Geographic about the terminal produced in 2005. You might want to get a copy of it.
Ed Gerson (Along The New Haven Line of Metro-North and Amtrak in New York State)