When people think of 1920s Chicago, stories of bootleggers, speakeasies, and Al Capone naturally come to mind. Part of the roaring ‘20s Chicago story are the Uptown tunnels, a network of underground passageways connecting the Green Mill Cocktail Lounge, several theaters including the shuttered Uptown Theater and the Aragon Ballroom, and other businesses in the city’s North Side.

Numerous theories about the tunnels’ purpose abound, largely surrounding the Green Mill, a 1920s speakeasy and now classic jazz club. It was founded as Pop Morse's Roadhouse in 1907, a place for mourners to gather after funerals at the two nearby cemeteries. In 1910, it was sold and renamed the Green Mill Gardens, complete with bathrooms in the basement.

During Prohibition, the bar became a speakeasy with Capone connections, so people theorize the tunnels were used to run alcohol up to the bar, fueled by the fact the trap door is still in use behind the bar and alcohol kept in the basement. Others claim the tunnels were used as escape routes during police raids; folks could scamper underground and emerge elsewhere in Uptown as if nothing happened. Other ideas suggest illicit card games and liquor storage.

But the tunnels were not built with booze running in mind. Bill Savage, Professor of Instruction at Northwestern University and prohibition historian, tells Mental Floss, “This is mythmaking, based on assumptions of organized crime that are not true.” The gangsters and bootleggers were not industrial engineers who built these specialized tunnels; They were making the most of Chicago's extant vernacular architecture.

Commercial properties typically have basements, and these tunnels are really more of a series of interconnected basements with doors, Savage says. And if a business took up more than one storefront on a block, it would have that many more basements connected by doors. Ric Addy, owner of the now-closed bookstore Shake Rattle and Read, reports that the tunnels were used for moving coal on rails to the furnaces in the basements. Addy led a tour of the tunnels in 2007, showcasing the bathrooms.

The gangsters likely used the Uptown tunnels to bring in moonshine and other liquor, and as an exit if and when the Green Mill got raided. But the stories about tunnels running all the way to Lake Michigan (over a mile away) are not true, Dan Pogorzelski, writer and editor of Forgotten Chicago, tells Mental Floss. Some assert the tunnels go under the streets to the nearby Aragon Ballroom and Riviera Theater. However, Savage believes these claims are also likely exaggerated. Parts of the basement network are now blocked off, notably the door leading to the now-shuttered Uptown Theater, built in 1925 and considered one of the largest theaters constructed in its time.

The Uptown tunnels aren't the city's only subterranean passageways. Chicago is home to tunnel networks across the city, most notably the Pedway in the downtown area that commuters and tourists alike often use to escape the elements. There's also the underground streets of Wacker Drive, made famous by The Dark Knight (2008). Other parts of the city have tunnels as well, such as Avondale’s long-shuttered Klaus's Department Store, which had a tunnel to different parts of the buildings, Pogorzelski says.

Despite the tunnels’ many non-Prohibition links, the lore surrounding them remains strong. According to Savage, there’s a tendency to romanticize the bootleggers; rather than view them as criminals, people like to see them as Robin Hoods providing people with what they wanted in a time of unjust laws. There’s also a desire to ascribe greater meaning to architectural details. For instance, it’s not uncommon for people to see back entrances or passages as built for the purposes of booze-running even though they long pre-dated Prohibition, just like the Uptown Tunnels.

People also like to claim Capone connections to places that may be loosely linked to the famous mobster throughout the city, Pogorzelski explains. Humans like to feel connected to the past, and these stories help people find the connection. He says the Green Mill represents the 1920s to both Chicagoans and tourists, much like how people want to see where Greek philosopher Socrates walked in Athens.