There's a small lake on old maps of MKE just ashore of Lake Michigan Downtown. When urban development started building up the Downtown area, instead of draining Lake Emily, the Northwestern Mutual building at Wisconsin and Cass was built on top of it. The huge log pilings were driven into the lakebed and still support the building today. The water level is maintained by the building's facility team, because if the logs dry out, they'll rot and the building will fall. The only glimpse of Lake Emily now is through the small holes used for checking the water level.
UWM Utility Tunnels
Many students at UWM have probably heard rumors of a network of tunnels under the school campus, and they're pretty much all true. The tunnels, constructed in 1968, connect the various school buildings with the central heating and chilling plant. There are miles of pipe that run through them, carrying steam to heat the buildings and other utilities. The tunnels were inspected and repaired in 2010, so students can try to break into them for many years to come (not that we, uh, recommend this).