A man in a navy windbreaker is telling me about the paved area that runs north-south between the two halves of the downtown Marshall Fields, one of the few privately owned “alleys” in the Loop. “Field’s has to close it off to traffic once a year,” he says. “It’s like the Rockefeller Center in New York. You know how that works? They have to close that outdoor area to the public for a day each year in order to keep ownership of it. One day every year. Otherwise it would be considered public property.”

De Wit moved here five years ago from the Netherlands, but his colleagues claim he knows more than any native about Chicago architecture and its history. Nevertheless, he tells today’s tour group to chime in or correct him when we can.

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“One of the things that makes these alleys special is the fire escapes,” says de Wit. “I think they’re beautiful. They make such interesting spaces.”

West of LaSalle, the alley whose line continues east through City Hall has walls covered with old signs. “Old Vienna Pastries, Sodas, Sundaes” goes the faded lettering on one. “Garden Lounge–Pleasantly Relaxing–Your Favorite Potion Properly Prepared,” reads another.

But then the tour is over, and we start heading back toward the Cultural Center. “This is the best view I’ve had of Bloomingdale’s,” says a woman in a flowered dress, as we approach the Clark Street bridge. Down below, on the river, a boat named Sunliner goes by, and overhead the dark clouds drift and regroup.