Nicola at Edible Geography recently published a fairly long, fairly detailed blog posting about salt therapy, salt caves, and halotherapy. Like many similar articles, details the history of salt caves and mines, speleotherapy, and even points out that in some countries salt cave sessions are even available on prescription.
The article talks about the growing number of salt caves in the United States, the different kinds of salt that they are using, and offers a variety of pictures from around the world of different salt-related caves and mines.