Five ordinary mining towns whose most valuable asset turned out to be the rock over their heads — a kilometre or two of it, enough to shut out the sky so that physicists in the workings below could sit in the dark and wait for the rarest events in the universe.
The Homestake workings reopened in 2007 as the Sanford Underground Research Facility. On the 4,850-foot level, under about 1,500 metres of rock, sits the LUX-ZEPLIN dark matter detector — and the same level once held Ray Davis's tank of 380,000 litres of dry-cleaning fluid, whose missing solar neutrinos earned him a share of the 2002 Nobel Prize in Physics.
Under the massif to the northeast, entered by a side road off a ten-kilometre motorway tunnel, lie the Gran Sasso National Laboratories at Assergi — the largest underground physics laboratory in the world, with 1,400 metres of rock overhead. It was here in 2011 that the OPERA experiment appeared to clock neutrinos beating light; the culprit turned out to be a loose fibre-optic cable.
A kilometre inside Mount Ikeno, in the Mozumi workings of the Kamioka zinc mine, stands Super-Kamiokande: 50,000 tonnes of ultrapure water watched by more than 11,000 photomultiplier tubes. Neutrinos caught in this mountain won shares of the Nobel Prize in Physics in 2002 and again in 2015. The same mine's cadmium poisoned the river valley downstream for decades — the cause of itai-itai, 'it hurts, it hurts' disease.
Some 1,100 metres down in the Boulby mine — the world's only working polyhalite mine — reached by a long cage descent and a drive through tunnels of salt, is the Boulby Underground Laboratory, Britain's deep-underground science facility. It has hosted dark matter detectors since the 1990s, and now grows salt-loving microbes for astrobiologists rehearsing the search for life on Mars.
Two kilometres down in Vale's Creighton nickel mine sits SNOLAB, the deepest clean-room laboratory in the world. Its predecessor hung 1,000 tonnes of borrowed heavy water inside a 12-metre acrylic sphere and showed that solar neutrinos change identity on the way here — work that gave Art McDonald a share of the 2015 Nobel Prize in Physics.
Think you'd have found them? Play today's expedition, or replay this one from the archive.