Salt well

A salt well (or brine well) is used to mine salt from subterranean caverns or deposits. Water is used as a solution to dissolve the salt or halite deposits so that they can be extracted by pipe to an evaporation process, which results in a brine or dry product for sale or use. In the United States during the 19th century, salt wells were a significant source of income for operators and the government. Locating underground salt deposits was usually based on locations of existing salt springs.

In mountainous areas, a similar technique called sink works (from German sinkwerk) is used.

...
Wikipedia