Minnesota, home of the massive neutrino

I once visited the Soudan mine with two young children. I try not to think of the background radiation from all that granite.

It's famous now:

BBC NEWS | Science/Nature | Light shed on mysterious particle

A high intensity beam of these particles was fired through a particle detector at Fermilab, and then to another particle detector 724km (450 miles) away in a disused mine in Soudan, US.

. The mine tour doesn't visit the lab, but you can see the locked entrance. It is a spectacular tour, but it is not for those who suffer from fear of bats, the dark, loud noises, enclosed spaces, heights (the elevator ride!) or mad, sadistic, tour guides seeking revenge on the bourgeoise for the sufferings their fathers endured digging dirt for distant capitalists.

Aside from that, I highly recommend it. Don't be fooled by those innocent and cheery looking tour guides by the way. You'll learn their true nature soon enough ... I swear ours cackled when she described how long it would take to climb the ladder to the surface ...