Many U.S. cities have some sort of hidden underground. Seattle has its underground downtown, Portland has its Shanghai Tunnels, Kansas City has a 5 million square foot office and industrial complex inside a network of reclaimed limestone mines, and Cincinnati even has a sealed-off subway system (with six completed stations) that never opened for business.

Given the number of hidden urban undergrounds around the US, I had to wonder whether my hometown — Milwaukee — has its own secrets beneath street level.

Deep Tunnel

Deep in the bedrock 130 feet below Milwaukee lie 19.4 miles of tunnel large enough to drive a truck through — the Deep Tunnel sewer project. The Milwaukee Metropolitan Sewerage District (MMSD) began the Deep Tunnel project in 1977 in an effort to reduce the sewer system overflows that occurred after most major rainfalls. The first phase of Deep Tunnel opened in 1993, phase two opened in 2006 and phase three was completed in 2010.

Although overflows still occur, Deep Tunnel reduced their number from as many as 60 per year to just 2–3 per year. In fact, during the years 2003 and 2012 there were no overflows. MMSD estimates that between August 1993 and August 2013 Deep Tunnel kept 98.7 billion gallons of wastewater out of Lake Michigan.

So should Deep Tunnel be on your “Milwaukee Sites to See” list? Although at the height of construction over 1,000 construction workers had access to this part of underground Milwaukee, today Deep Tunnel visitors are limited to an occasional handful of inspectors. Simply entering Deep Tunnel is a major undertaking. First, the air in the Deep Tunnel must be checked remotely to ensure that the oxygen level is high enough that inspectors won’t lose consciousness, as well as to ensure that there hasn’t been any buildup of explosive gasses. During the entire time inspectors are in the Deep Tunnel, a specially trained Milwaukee Fire Department emergency team is on standby and a special six-wheeled vehicle (which can both drive and float) is placed at the access point nearest to the inspectors.

Fun Fact: The island just off Summerfest where Lakeshore State Park is located was created entirely from bedrock excavated during the construction of the Deep Tunnel.

Lake Emily (beneath the Northwestern Mutual Building)

When searching for underground Milwaukee, one of the stranger tales is that of Lake Emily, an underground lake supposedly located below the iconic Northwestern Mutual building on East Wisconsin Avenue. Lake Emily’s existence has all the hallmarks of being an urban legend, but there is a factual basis for the story.

Early Europeans settlers built homes and a lighthouse near a small lake located where Northwestern Mutual’s headquarters currently stand. When Milwaukee’s downtown began to grow in the 1880s, engineers attempting to fill in Lake Emily discovered the lake was connected to an underground river, meaning any fill dumped into Lake Emily was just washed downstream into Lake Michigan. One version of the story claims that a diver sent by the engineers into Lake Emily disappeared and his body was found four days later floating in Lake Michigan.

“That lake is still there,” stated Milwaukee County Historical Society curator Theodore Mueller in 1952. “It has never been completely filled in because of an underground river.“

When the Northwestern Mutual building was constructed in 1912, according to Mueller’s version of the story, the building engineers simply laid a concrete slab over the lake and continued construction of the building. So does Lake Emily still exist under the concrete on the east end of downtown? In July 2013, OnMilwaukee.com editor Bobby Tanzilo was granted access to Lake Emily by Northwestern Mutual facility management. What Tanzilo discovered is that Lake Emily still can be glimpsed through 74 observation holes in the basement floor. The lake now exists in isolation below that thick concrete floor. Tanzilo’s article details how the construction of the building involved much more than simply placing a concrete slab over the water and explains why Northwestern Mutual continues to maintain Lake Emily — it is an informative read.

Neighborhood Prohibition Tunnels

In 1918, Milwaukee was home to over a dozen breweries and 1,980 saloons (one saloon for every 230 residents), so Prohibition meant significant changes for the city. Given the integral role alcohol played in Milwaukee’s economy and society at that time, temperance advocate Carrie Nation is quoted as saying, “If there is any place that is Hell on earth, it is Milwaukee.” One side effect of Milwaukee’s adjustment to the Eighteenth Ammendment was the creation of a number of smuggling and speakeasy tunnels in various neighborhoods.

The building that stood on the corner of 5th and Cherry served as home to several breweries following its construction in 1854, including the Jung Brewery in the years leading up to (and apparently during) Prohibition. When the City of Milwaukee took ownership of that building in 2001 (due to unpaid taxes), inspectors discovered a freight elevator that — when lowered into the basement — sealed flush with the wooden main floor, completely hiding the existence of both the elevator and the basement. Vaulted tunnels made of cream city brick led from that basement under the street, and at least one tunnel apparently connected to another nearby building. The former brewery building was demolished in 2007, but in 2010 Discovery World archeologist Kevin Cullen used ground-penetrating radar around the building’s perimeter to confirm that the building’s “sub cellars” are still in existence about ten feet below street level.

Rumors of tunnels and underground speakeasies are associated with a number of Brady Street buildings dating back to Prohibition, but concrete evidence usually is fleeting. Supposedly a speakeasy space extended underneath Brady Street from the basement of the Roman Coin, while the building at the intersection of Brady and Farwell (currently housing Starbucks and other businesses) is rumored to have held Prohibition era smuggling tunnels, as well as a speakeasy frequented by Al Capone.

What else may lie beneath our feet?

Have you experienced any locations that could qualify as underground Milwaukee? Is your basement connected to a secret smuggling tunnel from days gone by? Please share your experiences in the Comments below.