Another place that I visited in Transylvania was the town of Torda, where there is a huge (1200 metre thick) salt deposit that formed about 18 million years ago. The salt can be found forming the sides of a nearby valley where it has been eroded by rainwater into pinnacles.
The salt is 99% pure and the crystals form cauliflower like surfaces covering large areas.
The high relative humidity, constant temperatures, absence of dust and high concentration of sodium chloride particles in the chambers are regarded as beneficial for sufferers of breathing disorders (eg asthma, allergies etc). Large areas are equipped with playgrounds, a restaurant, internet access and even a church so that visitors can spend days at a time underground.