The 42 Street-Grand Central Lexington Avenue Line Station has two busy island platforms for the four-track line. These platforms opened on July 17, 1918 with the rest of the northern half of the IND Lexington Avenue Line. The Shuttle platforms is the location of the original subway station from 1904. Portions of the connecting corridor from the mezzanine above this platform to the Shuttle is along portions of the original track bed. The station is located on a diagonal, not directly beneath the street grid as the subway curves from running beneath Park Avenue over to Lexington Avenue to continue uptown. This means the 'southern' exits are for Park Avenue and 42 Street, northern exits for Lexington Avenue. The station lacks normal exits (the only one at the station is to Madison Avenue from the Shuttle), all set within buildings or through building lobbies.
In terms of design, the platforms have numerous large, white tiled wall columns with 42s in them and dual contract era mosaic trim lines that are mostly grey. The walls of the local tracks have similar trimlines with small hard to spot mosaics of steam engines representing the train station above (although all trains into Grand Central Terminal have always operated via electricity, with stream locomotives changing out at various locations north of the station). Above the platforms is a large, nearly full-length mezzanine that was renovated in the early 1990s. This means it has a slightly unusual design with walls of large pink tiles, columns that are round and a silver color and many fare control areas have non-standard silver fencing that doesn't reach the ceiling (maybe 7 feet high). The floor is mainly pink tile but some coloring exists in the form of an extra large compass rose in the middle of the mezzanine floor. The uptown platform has 6 staircases, the downtown platform 5 between the mezzanine and this platform as well as an elevator (towards the middle of each platform). In addition two staircases lead from the middle of the platform down to a passageway that continues to the 7 train's island platform deep below the other two subway stations, allowing passengers transferring between 4,5,6 and 7 trains to avoid going upstairs.
The mezzanine has numerous exits and transfer passageways:
Starting at the southern end of the mezzanine is a fare control area which leads up to two staircases to the street: one leads to 125 Park Avenue, reaching an intermediate landing and passing a shoe repair before leading up to two staircases on Park Avenue between the main ticket office and sidewalk for the buses to all three New York Airports; the other leads up to 110 East 42 Street between Park and Lexington on the south side of the street. This same building (they meet before the archway out to the street beneath a nice old fashioned Subway sign) has an exit only exit to it as well with a Exit High Turnstile (open weekdays 6am to 7pm) on the east side of the mezzanine right next to the far escalators down to the 7 train lower passageway. This that leads to an up escalator/staircase in the Bowery Savings Bank Building, 110 East 42 Street, and passengers reach the same inside building exit to the street.
Continuing with exits along the eastern side of the mezzanine, passing the two escalators down to the 7 trains lower mezzanine is a small, unstaffed bank of turnstiles, open 6am to 7pm Monday to Friday. Next to these turnstiles is the platform elevator for the 7 train platform. This exit leads into Chanin Building (122 East 42 Street) through revolving doors and into a small shopping arcade where a staircase leads up to the main lobby of the building beneath a simple sign. To leave the building you simply walk out to the street. There are no signs indicating there is a subway entrance inside the building.
Backtracking to the western wall of the mezzanine towards at its southern end is the main, wide walkway within fare control to the 42 Street Shuttle. This mezzanine runs along the trackbed of the former express tracks of the opening day IRT and has the shuttle platform's tile scheme. Near the western wall of this mezzanine are two escalators that lead (via an intermediate landing where they shift 90 degrees) down to the 7 train platform. Next to the Shuttle passageway is a very wide bank of turnstiles with the 24-hour token booth. From here there are steps up to an out of subway fare control but subway tiled passageway (it has the same tile theme as the shuttle platform) to the Shuttle platform entrance and entrances at Vanderbuilt Avenue and 42 Street (and access into Grand Central's Shuttle Passage). Next to the subway passageway, wide staircase, and escalators lead directly up to the 42 Street Passage of Grand Central Terminal, just before doors out to Pershing Square beneath the Park Avenue viaduct. There is also the ADA 'street' elevator from here that leads to an upper landing inside the 42 Street Passage next to the doors out to the street from the terminal. There is no direct access to the street from this exit (the busiest of the subway station) all exits are through Grand Central Terminal.
Continuing north of these exits, are the two platform elevators (to the 7 car from the front of downtown train) down to each platform. These are along a wall on the north side of the mezzanine as it briefly gets narrower and continues situated only above the uptown platforms. It expands again to its full width to the final smaller, northern fare control area with 2 staircases down to each platform towards their northern ends. Here is a bank of turnstiles and token booth (open most hours of the day) at the end of the mezzanine. On west side of this fare control area is a staircase up to Grand Central Terminal's Lexington Passageway (a much less hectic way to enter the building compared to the main entrance). On the opposite side a staircase leads up within a building (in the middle of the storefront for the store Strawberry) near the NW corner of Lexington Avenue and 42 Street and an underground passageway that leads into the concourse of the Chrysler Building (with a nice mosaic indicating the exit ) the main exit from here is through a bit of a shopping arcade with subway written on the 42 Street side of the building.