The world's very deep underground laboratories offer access to the ultimate in quiet environments for science research. Here the term quiet generally refers to the cosmic-ray muon flux that is greatly reduced in these laboratories compared to that at the surface. It is this feature that allows observation or searches for very rare fundamental physics processes, impossible to undertake on the surface because of the muon-induced background. Perhaps most notable of these is solar neutrino physics, for which, after a long history, Ray Davies received in 2002 with Masatoshi Koshiba the Nobel prize for measurement of neutrinos from the Sun. Such work falls firmly within the field of Particle Astrophysics—the use of particle physics to study astrophysics and of astrophysics to study particles.