I walked into the odd cave saddled with anxiety and congestion from severe allergies. Less than an hour later, I emerged feeling relaxed and much clearer. The secret? Salt. Nearly 13 tons of the stuff, all of it imported from Pakistan. Since at least the 19th Century, people have used salt — more commonly saltwater immersion — to cure or manage symptoms of migraines, arthritis, and much more. But salt caves are designed to concentrate the healing effects; 45 minutes spent in a Himalayan salt cave (even one built in Central Jersey) can be as effective as 20 hours floating in saltwater.