It was here in 1942 that the US tested their first atomic bomb in what was then under the seating at the University of Chicago's American football stadium. They have since turned the space into a library with this peace monument in the exact location where the bomb was detonated. It was all under the direction of Robert Oppenheimer.
https://www.uchicago.edu/features/how_the_first_chain_reaction_changed_science/
https://www.uchicago.edu/features/how_the_first_chain_reaction_changed_science/