The photo above shows the site of the Soudan Underground Mine. This was the oldest iron mine in Minnesota, opened from 1882 to 1962. In 1965 the mine was donated to the State of Minnesota to use for educational purpose and can be visited, down to the lowest level (the 27th, 2341 ft below ground) as part of a historical tour.
The crusher, Soudan Mine (Jun 6, 2013)
To take advantage of the low cosmic-rays background, the mine is also the site of the Soudan Underground Laboratory, a high energy physics lab hosting the MINOS and CDMS experiments. While CDMS is a dark matter experiment, MINOS is designed to measure the parameters of neutrino oscillations, the phenomena according to which neutrinos change their "flavor" as they travel. This oscillations are a consequence of neutrinos having a non-zero mass, which is something not predicted by the Standard Model of particle physics. Studying neutrino oscillations is thus a way of studying physics beyond our current working model. MINOS is one of the experiments in which Mayli is working, which is why we went at the mine site on Thursday as part of her collaboration meeting "tour". Mayli and I didn't go underground (we had been there in other occasions), but I never had time before to explore the mining equipment on the surface, including the "crusher" (inset photo on the left) used to literally crush the iron ore once it was hauled to the surface. The bit towering structure in the top photo is the surviving mine shaft, which is still used to lower the elevator cage all the way down, to access the lab and the mine level still open for the public tour.