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.”

We are sitting on the steps that lead from Randolph Street up to the Public Library Cultural Center, waiting for the rest of our group to arrive. The occasion is a tour of some of the city’s alleys, and the guide is Wim de Wit, exhibitions curator at the Chicago Historical Society. De Wit curated the “Chicago Streets” exhibit currently on display at the society, and as an adjunct to the exhibit he has led various tours of the city’s streets. But “that didn’t seem like enough,” he says, and so he organized this tour.

“We normally don’t pay attention to alleys,” he tells us when our group is complete. “We walk right by them without even looking for traffic. But they’re just as important to the city as its streets.”

Most downtown alleys, he explains, were built after the fire as access roads for deliverymen. In other cities, “alleys” were often the streets where poor people lived, but not in Chicago.

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.

It’s been raining off and on all day, and most of us clutch umbrellas as we trudge through the puddles along Randolph. Our first stop is Garland Court, the alley that runs north-south next to the Cultural Center.’

“It’s not really an alley–it has a name–but it functions as an alley,” says de Wit, and points out the Dumpsters next to the building and the four fire escapes on its side. For an alley, Garland Court is fairly wide; despite the long row of cars parked perpendicular on one side and the car with its hazard lights blinking pulled over on the other, there’s still plenty of room for an intermittent stream of traffic to barrel through.

Something else about the alley seems wrong, too, and de Wit tells us what: the west wall of the alley has an embellished facade, with false dormers over the windows and intricate carving around them, like the front of the building. Usually walls facing the street are fancy and walls facing the alley are plain. But this wall, de Wit explains, originally faced a park, not an alley.

South of Washington, Garland Court gets narrower. It’s a real alley now: used paper cups and empty potato-chip wrappers sit in the puddles, and fire escapes cover the sides of the buildings in spidery black geometric shapes.

“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.”

There are alleys in some parts of the city, he says, where the original wooden pavement still exists. None in the Loop, he says, but tells us to watch for other evidence of original construction. Signs along one wall of the alley that runs right through Carson Pirie Scott advertise carriages and shoe lasts; they’re old, de Wit says, but probably not as old as the building. On the same wall, at the north end of the alley, is the wide metal outline of a double door. The space has long since been bricked in, just like the spaces above it where windows used to be. The fire escapes are thick here too; the sky is barely visible through the tangle of black lines. The air in the alley feels warm and dry almost like we’re inside.

The alley ends at Monroe, but across the street in the Palmer House a wide indoor atrium continues south along the alley’s course. “It’s sort of a halfway public, halfway private space,” de Wit tells us. “Think about what the space really is: a modern version of the alley.”

De Wit likens the layout of the city’s alleys to the layout of its streets. Both form a grid, he says; even when alleys end, indoor paths–like those in the Palmer House or City Hall–continue the pattern. An alley south of Monroe running east from State, for instance, continues in the line of another Palmer House atrium. As we walk through this alley, named Marble Place, to Dearborn, the glowing red Berghoff sign is visible across the construction site at State and Adams.

As the city builds more and more megastructures like the Palmer House, more and more alleys will disappear, says de Wit. He particularly regrets the shopping center scheduled to go in between State and Dearborn, Washington and Madison, and he leads us over to Daley Plaza to look at some of the pretty buildings due for demolition. The pigeons rush over our heads, a fire engine screams down Clark, and the pigeons come back the other way. “The United Artists theater is beautiful,” says de Wit.

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.

The downpour starts as the tour group crosses Wells. We raise our umbrellas and duck under an overhang in the alley as it continues west. A tall man in a green suit stops picking through a Dumpster and comes to share our shelter. Above us, a glass tube connects the upper floors of two buildings.

“This is sort of the step between the older alleys and the new megastructures,” de Wit says: The alley makes a 90-degree turn in the middle of the block and then ends as it reaches a loading dock, discouraging public use. Unlike the older buildings, this one has the same plain surface on its alley side as it does on its street side.

The rain eases as we walk up Franklin, but the group is tired of the muck and the damp, and the tour has started to run over the estimated hour and a half. A few people turn back, and the rest of us head across the Franklin bridge to look at the dirt “alley” that crosses under the Ravenswood el tracks just north of the river. We fail to drum up the proper appreciation. “Look, the sewer is backing up,” says a man wearing a clear plastic raincoat over his clothes, pondering the concentric circles that bubble up through a big brown puddle. His wife comments on a missing segment of fence that has been patched with a piece of flimsy plywood.

Our spirits brighten a few blocks later, though, when the sky brightens from a dark gray to almost white. We practically get a second wind when de Wit feeds us a few historical tidbits: the rounded metal hump that looks like a rusty boulder at the Wells Street entrance to the alley between Hubbard and Illinois is meant to keep cars from running into the wall there, and cement embankments in an alley a few blocks away serve the same purpose. In between the two, along Clark Street, we pass a whole row of perfectly preserved 19th-century buildings.

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.