Deep TunnelPhoto: Jose M. Osorio/Chicago Tribune

Chicago is home to some of the greatest engineering feats in the world. Like the skyscraper? Yeah, that. But some of our most impressive technical accomplishments have come not from reaching toward the sky but from wallowing in the muck.

First, we had to build a sewer system in a swamp. To do so, the city lifted its buildings—with great teams of workers manning jacks, raising the structures slowly enough that business could continue inside—so that waste had a direction to go in.

That direction was the Chicago River, and then Lake Michigan, where we also got our fresh water. So when all that effluvia started contaminating our supply, we built offshore intake cribs—those funny little circular structures way out past the lighthouses—that pumped clean water through 60-foot-deep tunnels designed by the brilliant engineer Ellis Chesbrough.

But as the city’s population—and the volume of its sewage—grew, two miles out proved to be not far enough. So in 1892 the city started constructing the Chicago Sanitary and Ship Canal, moving more earth than the builders of the Panama Canal. The canal crossed a low ridge 12 miles west of the lake, creating the gravitational differential needed to reverse the course of the Chicago River so that its waste stopped draining into the lake and went instead into the immense Mississippi River.

Even that would be insufficient to keep Chicago from occasionally being flooded with its own dirty water. So in 1975 the Metropolitan Water Reclamation District began building the Deep Tunnel, a 109-mile system of massive underground reservoirs reaching widths of 33 feet and buried 350 feet down—an 18-billion-gallon storm drain.

Chicago’s epic of excrement wouldn’t be complete without the world’s largest water treatment facility: the Stickney Water Reclamation Plant, a 413-acre installation in Cicero that treats 700 million gallons (about 1,400 Olympic-size pools’ worth) of wastewater a day. But the plant doesn’t just reclaim water. It’s also the largest nutrient recovery facility in the world, keeping phosphorus—a waste-processing byproduct—out of the waterways, saving it for the farm fields of the Midwest.