If you've lived in Pittsburgh long enough, you've likely seen a never-ending shortage of artists renderings of proposed construction projects and infrastructure improvements including everything from Maglev stations to Clemente Field, many of which appeared in this paper but never came to fruition (or if they did were in drastically different form than originally proposed).
A friend that's even more of a geek about Pittsburgh history than myself sent along this link to a 1958 proposal for what eventually became Three Rivers Stadium.
Behold the wonder:
Here's the write up that goes along with it:
"The Proposed Stadium over the Monongahela. A Classic Structure that will blend with the Renaissance of Pittsburgh. Completely Self-Liquidating. No Tax Loss. No Land Acquisition. 70,000 Capacity with Majority Under Cover. 600 Room Hotel with Gourmet Restaurants. 4,500 Automobile Parking Stalls Inside. 100 Air Conditioned Bowling Alleys. World's Largest Covered Boat Dock. Beautiful Gardens Overlooking River. Truly a Multi-Purpose, Multi-Income Facility. A 'First' in the World. Consulting Architect: M.de Mailly of Paris, France, Premier Grand Prix de Rome Winner. Idea Originated by Mr. Eric M. Sirko."
Forget that not only did this not happen and that (at least based on this drawing) the Smithfield Street Bridge and the Pennsylvania & Lake Erie Railroad Station (now Station Square) would have to have been knocked down to accommodate it. Pretend for a moment that some form of this plan was actually a go, I honestly cannot decide if Pittsburgh missed out a truly iconic feat of engineering or was spared a monstrosity of epic proportions.
Worth mentioning -- another early sketch of Three Rivers indicates that it very well could have been an iconic building, rather than the cement ashtray eyesore that it was, and perhaps not only would not have outlived it's usefulness so quickly, but would remain an architectural classic.