An ear popping experience!
Once upon a time, the sea extended all the way back to Krakow. During the last ice age, when sea levels went down, large bodies of water were trapped by the continents. Over many years, the water evaporated and, having no river flowing into it, left behing a very large area of salt, like the Uyuni Salt Flats in Bolivia. It was mined for 800 years before going out of operation. It’s been a tourist attraction since the 15th century, with its beautiful salt cathedral (everything sculpted from salt, including the chandeliers). Notable visitor include Copernicus, Goethe and Chopin! Worth a visit!