There are underground passages at Grand Central Terminal in NYC that are open to the public. They fan out, underground going several blocks from the main terminal, both north and west. Many people use them each day. The passages are useful when it is raining or very hot or cold outside. However, it seems not all tracks provide access to all the passages.
It seems some tracks have an exit at the northern end direct to either the northeast or northwest passage. Other tracks have an exit to the 42nd St east west passage. There seem to be some connections between these passages.
It seems the 42nd and 45th St passages go east west and are one flight below the northeast and northwest passages.
Where can I find a map of these passages, that shows where they have exits to the street above and which tracks have access to the several passages?