That’s the beginning of the construction of Grand Central Terminal, in 1908. To place everything, both the second and third (current) Grand Central straddle Park (Fourth) Avenue on the north side of 42nd Street. This picture was taken from approximately the line of 45th Street, a half block east of Park Avenue, looking south.
Grand Central was (and is) an extremely busy station, so it was kept in operation the entire time that the old station building was demolished and the new one built. Those trains on the right side of the picture are parked at platforms that were in use at that time. The amount of excavation has a simple explanation: the old train shed and platforms were at grade; the new station has two levels of platform (one directly above the other) and the upper level is about one story below grade. The tracks were lowered in part because the approach, from 96th Street south, was in a tunnel below grade and in part to create directional flow for pedestrians within the station. The excavation on the left side of the picture has reached the bottom elevation. It proceeded in north-south-oriented strips, with new tracks built at the lower level and steel for the upper level put in place and then the new tracks pressed into service as soon as the excavation had moved on to the next strip. The use of a stable slope rather than sheeting is fine for excavation, but it does create that dramatic image of a train, some broken pavement, and then a thirty-foot-high slope down.
The two domes on the right mark the east and west ends of the main portion of the old station. In between the stub of the old train shed is visible: the shed was being demolished from the north to the south and originally would have covered the trains on the right. You can see the shoring in place to allow for safe removal, above trains and pedestrians, of the two-hinged arched wrought-iron trusses that support the shed roof. To the left of that, past the excavation, the gable shed roof that covered the later arrivals extension of the station is almost gone. The two curved mansard roofs mark the east and west ends of the arrivals extension and match the design of the first station, which was altered and expanded into the second station eight years before this photo.
The big building on the far left, seemingly up on stilts, is a new post office. Since mail was to be delivered by rail directly to its subgrade levels, the post office was built in coordination with the new station. This can be seen by a strange change in elevation: the dead end street on the left between the post office and the arrivals extension is Depew Place, a short street added to the grid when the rail yard blocked Fourth Avenue, and its northern portion has been removed. You can see the elevation at which DePew Place will be rebuilt by the bases of the ornate columns at the post office, and it’s well above the stub of the old street. DePew now slopes up from 42nd Street to meet that higher elevation.
The big building just south (to the right) of the post office is the Grand Central Palace, an exhibition hall built in 1893 and used briefly as a temporary extension to the station during the construction. It was demolished shortly after the new station was complete. The low rise build south (to the right of that), with the big square chimney was a factory. I’m not sure what was going on there in 1908, but a decade earlier it was making wallpaper. It was also demolished shortly after the new station was complete.
The very tall building on the right is the Hotel Belmont, on the south side of 42nd Street. The last few landmarks need a close up:
The squarish mansard between the two creed mansards of the arrival extension is the 1868 Grand Union Hotel, the first hotel to try to grab rail passengers when the first Grand Central opened in 1871. The blocky tall building behind that is the 1908 Terminal Building, a just-completed office using the name of the new station that had not yet been built. And finally, off in the distance, the steel skeleton of the Met Life tower at 24th Street and Madison Avenue can be seen between the main station and the arrivals extension.