Cornerspotted: Union Passenger Depot, Predecessor to Union Station

In the wacky world Cornerspotter, sometimes it's the 'spot' we deem obvious that produces the broadest sweep of guesses. This week's edition featured the original 1880s Union Station (full name: General Union Passenger Depot of the Chicago & Alton Railroad) on the site of the current one, but elicited reader responses of Merchandise Mart, East Bank Club, Palmer House, and Diamond's Gentlemen's Club (are we missing something?) along with several correct IDs. The station was the city's first "union" of rival passenger services, focusing energies on cooperation for the betterment of travelers who formerly had to traverse the downtown for transfers at various stations. Opened in 1881, the unification also meant fewer tangles of track inhibiting the organic growth of the city outward from the Loop. Growth in passenger traffic and a desire for further consolidation produced today's Union Station, opened in 1925.
·Hint: An Early Confluence of People and Commerce, Whose Site Retains the Same Use [Curbed Chicago]
·Union Station Coverage [Curbed Chicago]
·Chicago Union Station [Wikipedia]