Answer: Crude Oil Baths

Once among the hottest vacation spots in the Soviet Union, the spas of Azerbaijan are a curious place. While a trip to most spas might find you soaking in hot water, perhaps wrapped in seaweed, and potentially dunked in mud, the spas found in Naftalan, in the central region of Azerbaijan, specialize in dunking their visitors in bathtubs full of crude oil.

Yes, that kind of crude oil—unrefined oil pumped up from the depths of oil fields in the region. The tradition goes back centuries (records of crude oil seeping to the surface date back to the 13th century and locals have been finding creative uses for it ever since) and is considered a useful luxury hailed as a cure for everything from psoriasis to aching joints.

While some of the health claims associated with the treatment are certainly dubious, some have a fair grounding in science. Dermatologists, for example, do in fact prescribe special soap with naphthalene in it to help with psoriasis and the crude oil in the region has a very high concentration of that very compound (around 50 percent).

Speaking of the composition of the oil found in Naftalan; it might be crude oil through and through, but its particularly dense composition makes it poorly suited for refinement and it has little commercial value. Little commercial value that is, beyond being pumped by the barrelful into the local spas.