Actually it's a neutrino detector built one-thousand meters below Japan. The Super-K neutrino detector was the facility that more or less resolved the missing neutrino problem a decade ago. The sun produces billions and billions of neutrinos and hurls them towards Earth, but scientists were seeing only a fraction of what models predicted they should have been seeing. Experiments at Super-K proved that the shortfall was occurring because the electron neutrinos produced by the sun were transforming into other kinds of neutrinos - a significant finding because neutrinos need to have mass to oscillate, and because massive neutrinos may help to explain some of the missing mass in the universe.

Now the detector has been totally revamped and is set to contribute to debates about string theory.

Originally built in 1983, and renovated just last year, the Super-K facility engages in experimental research designed to reveal new information about cosmic ray physics, dark matter, and the number one task currently intriguing scientists worldwide--the creation of a Grand Unified Theory, a new theory that would unify the strong, weak and electromagnetic forces in the universe.

More importantly: it looks totally awesome.

References:
* Super-Kamiokande Facility
* Solar neutrino problem [Wikipedia]
* Dark matter research facility could double as science-fiction movie set [Sci Fi Tech]
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Previously:
* Best Movie Idea Ever
* Acapella Yumminess
* Doom On Your Calculator