Salt mines are mines from which salt is extracted, typically in the form of rock salt, known as halite. Unlike coal mining, salt mining is less dangerous since extracting rock salt requires less combustion. 

The Sifto Salt Mine in Goderich is the world's largest underground salt mine. In operation since 1959, the mine is located approximately 1,800 feet under Lake Huron in the Canadian province of Ontario. It stretches over 1.5 miles wide, 2 miles long, and covers an area of 2.7 million squares miles.

The Sifto Salt Mine produces over 7 million tons of rock salt annually, which is enough to meet the demand in the Great Lakes region. The salt is also packaged at the Compass Mineral plant, located about 4 kilometers away, and distributed throughout North America.

Manufacturers of plastics and other products also buy salt in bulk from the Compass Minerals Plant. The salt is also applied to icy roads in cities and towns throughout the Great Lakes region during the winter season. 

According to worldatlas.com