There seems to be a newfound fascination with the unbuilt. As urban planners are rethinking cities, historians of art and architecture are delving into the past, plucking from archives artistic renderings of residential communities, airports, transit systems, even theme parks that, for one reason or another, never came to fruition.

In 2004, a curator at the Art Institute of Chicago gathered 80 drawings and models detailing the Windy City that could have been for "Unbuilt Chicago." The National Building Museum, in 2011, similarly presented a slew of monuments, bridges, museums and other structures—proposed, but never executed in the nation's capital—in its exhibition "Unbuilt Washington." And, most recently, the A+D Architecture and Design Museum took on Los Angeles, playing host to "Never Built: Los Angeles," a show featuring more than 100 stymied projects.

"It blows your mind," says Sam Lubell, co-curator of "Never Built: Los Angeles" and co-author of its accompanying book. "You think LA was always going to be a freeway city, it was always going to be a sprawling metropolis, but no. Things could have been extremely different."

Designers, in the last century, dreamed up complex green spaces, aquatic theme parks and airport helicabs.

"L.A., maybe more than almost anywhere, has this amazing capacity to imagine the future. And it has the talent to do it," says Lubell. He references the film industry and aerospace. "It is just a place where people go to be different. For better or worse, they go to dream."

Lubell and Greg Goldin, a curator at the A+D Museum, salvaged some of these squashed dreams from city archives, UCLA and the Getty Museum, among other collections. The projects reveal an alternate history, an unfamiliar skyline. But, more so, says Lubell, the bold plans beg city planners, considering today's architectural schemes, to ask an important question:

Are we too timid?