Many of particle physics' most interesting observables (neutrinos, dark matter, proton
decay) require detectors installed underground. In many cases, the constraints
associated with mines---limited roof spans, limited sites, safety, and excavation costs---
are beginning to limit the scope of our experiments. The energy and chemical industries
have 100 years of experience with a different type of underground space: solution-mined
salt caverns. These are obtained by drilling into large salt formations and dissolving the
salt with water. The caverns obtained can be enormous, deep, stable and above all
inexpensive---but of course they have their own access and pressure constraints. In this
talk, I will argue that a wide range of desirable detector technologies, including giant gas
TPCs, might be deployed with these caverns. In particular, I will talk about an (untested)
TPC gas mixture I devised with these caverns in mind, but which may prove useful in
conventional labs too.