The UC Berkeley Library maintains a little online museum about San Francisco bay area bridges full of renderings of the bridges before they were built and photographs of them under construction.
This is interesting enough, but most fascinating is the Unbuilt Projects section, detailing bridges that were never built, including Frank Lloyd Wright's famous SF-Oakland span ... and some plans I'd never heard of to use systems of dams to turn most of the bay into freshwater lakes, waterways, and habitable land. Such plans would never pass environmental impact review today — and that's probably for the best.
And that makes me think of Jake Coolige's marvelous BART map for the completed BART system as it was imagined in the 1950s, ringing the Bay. The science-fictional-looking people who launched BART in the '70s seem like they might have been capable of building such a thing.
I marvel at the ambition of an earlier time, an ambition which we seem to have lost.