There are many mines, all over the world, producing any imaginable natural resource. Some are on the surface, like the Big Pit in Utah, USA, but most are deep inside the Earth. Some mines have thousands of years of history, others are very new.
Most of the mines are closed today, because their ore is not valuable enough, too expensive to get, or exhausted. And so, in many countries of the world, those mines were reactivated for various purposes. The most common one is a so called show mine or visitor mine, a sort of realistic museum of mining history, which includes an underground tour. Sometimes the emphasis is more on the museum, sometimes more on the underground tour.
Less common, but still important is the usage for healing. Several old mines are used to cure diseases. Speleotherapy, radon therapy, halotherapy and simple thermal baths are the most important. While speleotherapy actually is offered both in mines and caves, despite the name, the other two are restricted to mines.