The Suggental visitor mine in Denzlingen is always worth a visit. The mining research group Suggental has made several mining eras visible here.
450 meters of route are walkable. The former "Erich" pit is the only mine in Baden-Württemberg that has a surface pit. You have to register for guided tours, but in September there is the Stollen Festival, which includes visits.
Image courtesy of Stefan Asal - Datacreate Asal