Besucherbergwerk Kleinenbremen, Iron ore show mine and museum in Porta Westfalica, Germany.

Besucherbergwerk Kleinenbremen is a former iron ore mine in Porta Westfalica, open to visitors as a show mine, museum, and geological site. The underground tunnels pass through rock layers from the Cretaceous period, with traces of extraction work still visible along the walls and ceilings.

The Wohlverwahrt iron ore mine was worked until the 1960s, when extraction by Barbara Erzbergbau ended. In May 1988 a section of the disused mine opened as the Besucherbergwerk Kleinenbremen. The Wohlverwahrt pit was designated a National Geotope in 2006, placing it among Germany's most important geological sites.

The mine lies in Kleinenbremen, a district of Porta Westfalica, and its iron ore was mined by Barbara Erzbergbau until the 1960s. The affiliated Museum für Bergbau und Erdgeschichte shows how mining methods and miners' working conditions changed over time. The Wohlverwahrt pit was named a National Geotope in 2006.

Tours are guided and move through underground passages where the temperature stays cool year-round, so warm clothing is worth bringing regardless of the season. The ground can be uneven in places, and sturdy footwear is a good idea, especially for children or older visitors.

The underground lake is called the "Blaue Lagune" (Blue Lagoon). Sport divers were permitted to dive it from 2009 to 2018, making it a dive site as well as a sight on the guided tour. The mine's iron ore deposit, Grube Wohlverwahrt, was named a National Geotope in 2006.