Walking through downtown Chicago, one is surrounded by buildings that mark watersheds in architectural history. But few people know about the Chicago that could have been. From Adolf Loos’ spectacular proposal for Chicago Tribune Tower to Greg Lynn’s Stranded Sears Tower, Visionary Chicago illuminates more than 100 unrealized projects from the past century that continue to haunt and inspire the contemporary imagination. The collaborative project is an iPhone app–driven tour of fantastical schemes revealed at the sites for which they were designed. It’s an extension of the version that architects Irene Cheng and Bretty Snyder created for New York City in 2009. The Chicago edition is based on the research of local architect and writer Alexander Eisenschmidt, who describes it as “a directory of ideas, ideas of how to engage the city.”