Soudan Underground Mine State Park | Soudan, MN. 19th-century iron mine in boreal forests of Minnesota has been repurposed as one of the deepest physics experiments in North America—that's open to the public. In this subterranean lab, a neutrino detector looks for changes in subatomic particles emitted 460 miles away at the Fermilab particle accelerator. Another experiment searches for dark matter. Visitors take a three-minute mine-cage ride for a physics lesson half a mile below the Earth.