I think your thinking of FermiLab.
I live RIGHT NEXT DOOR to FermiLab, which was the largest particle accelerator for 20some years. It's not directly under Chicago either, because in order for an accelerator to work, I do believe there has to be empty space above ground.
FermiLab is in Batavia, IL. About an hour from Chicago. One of my best friends father works there. Very interesting stuff.
On a side note about FermiLab, for anyone who has been to Disneyworld. The Hotel that has the monorail through it? (I forget it's name) is the same identical design as the FermiLab building.![]()