Saturday fun activity: Where IS this?

     This photograph looks, to me, like an architectural drawing from the 1960s, of some ooo-the-future modern structure, dwarfing the obligatory human figures tucked in for scale. 
     Where is it? If you're thinking, "Can't be Chicago," you're on the right track. But a place enough Chicagoans have been to that there's a chance somebody will recognize it. 
     As for prizes, well, to be candid, winners have not been claiming them, so we can do away with the canard. If the person who guesses correctly wants one, they can ask, and we'll find something suitable. Which also makes me suspect that the Fun Activity has run its course, again, and it's time to retire it. Thoughts? Otherwise, place your guesses below. Good luck.