Sheri, Furnas, Sao Miguel

@Observing: Yes, I guess you could consider it cultural. Furnas is a town on Sao Miguel in the Azores. It is in an area that is active with geothermal energy. There are many hot springs and geysers. At one of the hot springs is a small cave and the locals believe it has therapeutic properties. They will sit in the hot springs. Then put the mud on their faces and bodies and allow it to dry and then rinse it in the hot springs again. They also believe the waters have healing properties. If I recall correctly, there are several tapped springs each with its own beneficial qualities. The local fill their bottles as needed.