That’s the Park Avenue Hotel, as seen shortly after 1900. It was located on the west side of the avenue (see below regarding addresses) between 32nd and 33rd Street, and was completed in 1877 after a period of construction that was exceptionally protracted, dragged out by economic problems. (Daytonian in Manhattan gives a nice history here.) It was torn down in the mid-1920s, and its site used for Eli Jacques Kahn’s fantastic Two Park Avenue (see below regarding addresses).
In general, cast-iron facades were used in New York for industrial buildings – most of SoHo being examples – but they showed up in a few hotels and department stores. Construction began before the Chicago and Boston fires of 1871 and 1872 got people thinking about fireproof construction, and was completed before New York’s first comprehensive building code was enacted in 1882. In short, the building was built in an era when nearly every building in New York had wood-joist floors and any iron used was not protected from fire. Daytonian quotes contemporary descriptions of the hotel being “absolutely fireproof” but it was not. Exposed iron facades may be non-flammable, but they are not fire protected. It had internal bearing walls making it not very much different, structurally, from a row of houses. Here it is on an 1890 fire insurance map:
The parallel lines are the interior bearing walls; pink was the color used for all ordinary construction at tat time: fireproofed construction was still so rare that it ws not yet differentiated on the maps. (Green was used to indicate special hazards, with the dots indicating the class of hazard. 35 East 32nd Street, could have had any number of light-manufacturing occupancies, including bakeries and blacksmiths, while 33 East 32nd had a higher-risk occupancy, such as a carpenters shop.) In general, the cast-iron front buildings we’ve seen from the 1870s have wood-joist floors, while some of them from the 1880s have tile-arch floors carried by wrought-iron beams. It is probable that the hotel had wood-joist floors. In short, the hotel had some degree of interior compartmentalization that might slow the spread of fire, but it was not fireproof. This is important to emphasize because in 1902, a fire killed 21 people there.
On a very different note, the Park Avenue Hotel was not on Park Avenue. Here’s a bigger piece of the map:
At that time, the name “Park Avenue” was used only for the stretch of the street between 34th Street and 40th Street, where the tracks leading south from Grand Central were decked over. Just below the map number “75” is a note reading “sunken tracks of the 4th Ave surface railway”, while open cut between 32nd and 34th Streets reads “tunnel approach.” Later, the name Park Avenue was applied to the entire street from 32nd Street north; still later, Fourth Avenue from 17th to 32nd Street was renamed Park Avenue South. If you look at the upper (close-up) map, the hotel’s address is 482 Fourth Avenue; the replacement building on the lot is 2 Park Avenue.
So the absolutely fireproof Park Avenue hotel was built of flammable materials and wasn’t on Park Avenue.