Salt therapy (or halotherapy, speleotherapy, salt cave therapy) is a form of alternative medicine which involves staying in a salt cave to breathe the air and treat respiratory problems. It's quite popular in Eastern Europe (Poland, for example, is renowned for its salt mines). Currently, not much research has been done on the subject, and the effectiveness of the treatment remains up in the air (no pun intended).
Halotherapy is related to salt lamp use, which involves lighting a candle or electric light inside a salt rock to "release negative ions". However, salt cave therapy could possibly work, while salt lamps are just woo.