Menthol Crystals. Place directly onto sauna stones or add to ladle full of water and pour over stones. These provide an eye opening blast of menthol vapor. Cleans out the bronchial tubes Do not keep bottle inside sauna as the crystals will melt. If the bottle does gets heated in the sauna it will turn to liquid and then harden as one piece. In this case, reheat in the sauna and then pour over a piece of tin foil and let cool. Next break these up and return to the bottle. They will now be flakes instead of crystals but still very usable.