Underground Chicago: Exploring The Hidden Layers of the City

By Alex Bean on November 10, 2017


When people think of Chicago architecture it’s very likely their first thought is of soaring skyscrapers. But the architecture of underground Chicago is fascinating and essential in its own right. Virtually unknown layers of tunnels, passages, sewers, pipes, and other infrastructure criss-cross below the city. Especially on a cold snowy day like today (perfect for an indoor walking tour with us!), let’s consider the (mostly) dry and warm spaces below our feet.

The Pedway System

underground chicago pedway tunnel
The Pedway tunnels allow pedestrians to wander the city below ground.

The most user-friendly layer of Chicago’s underground is the Pedway System, which we explore on our Loop Interior Architecture Tour. The term “Pedway” is a conjunction word formed from “pedestrian way.” A busy city like Chicago is always looking for ways to drop syllables for efficiency!

Functionally, the Pedway is a collection of basement-like hallways which connect buildings, train stations, and underground parking structures in the Loop. Small parts of the Pedway consist of “skybridges” that link the upper floors of adjacent buildings and passages that stay on the street level by cutting through lobbies.

You can also use our handy Pedway map to explore this essential layer of underground Chicago.

Underground Streets

underground Chicago lower Wacker Drive
Photo by Paul Sableman via flickr

The most viewed portion of underground Chicago underground is probably its underground streets, such as Lower Wacker or Lower Michigan. Movies like The Dark Knight and The Blues Brothers have immortalized these dark concrete spaces. But even locals often do not know exactly why this part of underground Chicago exists when we visit a section on our Historic Chicago Walking Bar Tour.

Our multi-layered city has lower levels of streets in some parts of the Loop and River North because it allows easy access for freight transport and trash disposal. That, in turn, make the street-level less crowded. Some sections, like East Randolph near Maggie Daley Park, which we spot during our Architecture Tour for Design Lovers, are even triple-decked.

A great thing about the multiple layers is that it keeps the trash away from where most people work, live, and commute. That means it keeps the rats away from pedestrian level as well.

Sewers of Underground Chicago

Underground the streets of Chicago, below the Pedway and below the underground streets, you will find the sewers. While no human should actually want to explore these, it is where our population of 2-3 million rats live.

It’s gross to imagine that many rodents, but it’s a reasonable number for a city of our size (you don’t want to know how many are in New York). Most cities have as many rats as human residents, if not more.

‘L’ Lines and Abandoned Freight Train Tunnels

Abandoned freight tunnels pepper underground Chicago. Image via Wikimedia

Along with the Pedway and the Blue and Red ‘L’ lines sits a set of abandoned freight train tunnels. Constructed in the early 20th-century, these tunnels transported coal and provided underground space for telephone wires. Newer and cheaper infrastructure passed them by in the 1950s and people began to forget they were even there.

It took a true Chicago fiasco to remind everyone they were there. A construction crew accidentally broke a hole in one of the tunnels in the early 90’s. That hole happened to be below the Chicago River, near the famous Kinzie Street BridgeWater came pouring into the tunnel and caused massive flooding in basements throughout downtown. The deluge ultimately caused more than a billion dollars of damage! Afterwards, the city installed watertight bulkheads to seal off the underground freight and cable car tunnels tunnels.

underground chicago water tower water crib tunnel
The iconic Water Tower drew fresh water to the city via a hidden 10,000 foot tunnel. Image via Wikimedia

Water Tower Pumping Station

According to WBEZ, the Pumping Station at the Historic Water Tower drew water from Lake Michigan via a five-foot tall brick-lined tunnel that ran underground and out to a water intake crib. The tunnel is more than 10,000 feet long and is still in existence, but the city refuses to comment on its exact location or current usage. So mysterious!

The Deep Tunnel System

The least-known or understood feature of the Chicago underground would be the TARP system, better known as the Deep Tunnel. In the city that lives by the mantra of “make no little plans,” the city has undergone one of the largest and longest civil engineering projects in American history.

It has cost billions and taken decades to construct the Deep Tunnel. Now that it’s functioning, it keeps stormwater runoff from contaminating the lake and prevent catastrophic flood conditions. The tunnels are often underneath existing waterways, like the Chicago River. They work to funnel excess water to reservoirs and run-off canals on the city’s edges.

You never quite know what’s underneath your feet in Chicago. Or what’s above you, for that matter.

– Amanda Scotese and Alex Bean


Chicago Detours offers guided walking and bus tours of architecture, history and culture to public and private groups. We are a passionate team of educators, historians, artists and storytellers, and are proud to be one of very few tour companies in Chicago that is rated five stars on both Yelp and TripAdvisor.

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