Red Gate Woods

Red Gate Woods is a forest preserve section within the Palos Division of the Forest Preserve District of Cook County, Illinois. It is located near where the Cal-Sag Channel meets the Chicago Sanitary and Ship Canal. In the woods is the original site of Argonne National Laboratory and the Site A/Plot M Disposal Site, which contains the buried remains of Chicago Pile-1, the world's first artificial nuclear reactor. 
This section of the forest preserves, then code named Argonne (after 
Forest of Argonne) was leased by county commissioners to the Manhattan Project (and later Argonne Laboratory) in the 1940s and 1950s. After its initial tests, the reactor at Stagg Field at the University of Chicago was removed and reassembled at the Metallurgical Laboratory site in these woods ("Site A"). Local residents reported encountering US Army MPs guarding the area during World War II but no one was aware of the true nature of the activities until long after the war. After further experiments and the shutdown of Pile 1, by then designated Pile 2, a huge hole was dug and the 2-story high reactor was pushed into it and buried ("Plot M"). Other reactors were also built at the site and nuclear waste was buried there. The site is monitored by the United States Department of Energy and is open to the public. 
Intervention from the Department of Ecology and Argonne National Laboratory cleared and cleaned the area by eliminating radioactive soil.
There is signage in the parking lot showing Albert Einstein and Enrico Fermi at the Red Gate Woods site during the Manhattan Project. Concrete markers designate historic sites and the foundations of Manhattan Project labs still exist.