Soudan Mine, Minnesota

The Soudan Mine would be simply superlative as the largest underground iron mine in the state at the time it closed in 1963, and became a state park, attracting tourists to its half-mile depths, but it has become an unusual high tech research environment as well, one of a handful of physics labs established in former underground mines around the country. Taking advantage of the infrastructure (elevators and electricity and such), part of the mine was leased to the University of Minnesota to house physics labs for research that requires isolation from the frenetic activity of the earth's surface. Two large chambers have been hollowed out at the deepest level of the mine supporting primarily two different experiments. One is the CDMSII (Cryogenic Dark Matter Search), studying dark matter - the unknown material which may constitute 90% of the universe. The other chamber houses MINOS (Main Injector Neutrino Oscillation Search), which is the receiving end for catching neutrinos injected into ground by a subatomic gun at Fermi Lab in Illinois, 450 miles away. In both cases the rock above and around the facilities acts as a filter for subatomic particles, allowing the smallest and hardest to detect ones to rise to the level of detection. MINOS, for example, uses a battery of massive octagonal sheets of energized steel to look for neutrino traces, a subatomic stop sign.