The great open-cast mine is the result of subsidence caused by mining techniques and exists since 1687. Mining was carried out in huge chambers, dug out one above another. Since this time, the "great shaft" (100m deep and 400m large) has become a major attraction. A lift takes you down to a depth of 55m. The circuit (approximately 600m) takes in some of the oldest chambers and galleries, as well as the shaft where mining began in 1662. Each shaft has a name and its own story.