Lunatide

The sole export off of Earth's semi-intact moon , Lunatide is a substance similar to water in its composition, but with a milky white, almost opalescent look to it. Looking straight at it, it shimmers lightly with the movement of the fluid, and can be almost hypnotic. Found only on Luna, it's drawn up from vast underground springs, and naturally occurring lakes and rivers across the surface. 

Lunatide's popularity comes from its abilities as a relaxant, but it's not something you ingest. Though I suppose you could. It's a topical remedy, used by private masseurs, parlors, VR palaces, salons, etc, as a far more effective (and expensive) alternative to something like a bath in warm water or oil. Once heated, Lunatide manages to leech tension from muscles, and soothe aching pains, making it popular with industrial workers, adventures, and the elderly alike. Many rich people maintain their own pools of Lunatide for their own pleasure, but also as a status symbol. No manor is complete without the stuff. 

As popular as it is, there is little to nothing known about the stuff. Its chemical composition is ridiculously complex, and as far as analysts can tell, it should be some sort of long-chain, not a liquid. It certainly shouldn't make up its own version of a water table on Luna's surface. Yet, it forms lakes and oceans, evaporates, then rains back down again, and can be found in aquifers deep underground. Luckily, the inhabitants of Luna don't seem exceedingly interested in fully tapping the Lunatide, allowing it to remain on Luna for visitors to enjoy. If it was anyone else, it would seem like they were trying to inflate the price, but anyone who knows the inhabitants of Luna, know they wouldn't do something like that.