Salzbergwerk Bad Friedrichshall Bad Friedrichshall · Baden-Württemberg · Germany

Rock salt in the Bad Friedrichshall area was first drilled in 1816 by Bergrat Bilfinger at Jagstfeld, at approximately 150 metres depth, demonstrating for the first time in central Europe a solid rock-salt deposit of this scale. On 16 April 1817, King Wilhelm I of Württemberg granted permission for a salt boiling house and for the sinking of a shaft. The Saline Friedrichshall opened on 14 January 1818; in 1820 it was formally constituted as the Königlich Württembergische Saline Friedrichshall. A first underground salt mine at Jagstfeld was successfully sunk between 1854 and 1859 under the direction of Friedrich von Alberti, geologist and salinist, making it the second rock-salt mine in Württemberg after the Salzbergwerk Wilhelmsglück near Hall. In 1895, however, inadequate pillars caused the collapse and flooding of the Jagstfeld mine. At the site of the former shaft, today a lake — the Schachtsee — now exists.

Following the Jagstfeld disaster, the Württemberg parliament resolved in 1895 to open a replacement mine in the Heilbronn area. Shaft-sinking at Kochendorf began in 1896, under the supervision of Bergwerksinspektor August Bohnert. The salt layer was reached in December 1899 at 151.5 metres. The Schacht König Wilhelm II., named after the reigning Württemberg king, was formally commissioned on 1 December 1899. In 1900 the salt boiling works at Jagstfeld and Rottweil, together with the new Kochendorf mine, were consolidated into the Staatliche Saline Friedrichshall. Guided tours below ground were offered even before the First World War.

During the Second World War, the mine's galleries were requisitioned for armaments production. From January 1944, the Reich Ministry of Armaments oversaw the conversion of the underground chambers into a bomb-proof factory for aircraft turbines and other military goods, under the code name Eisbär. From May 1944 the Hochtief AG and the Vereinigte Untertage- und Schachtausbau (Veruschacht) GmbH carried out the physical conversion. In August 1944, an outer camp of the KZ Natzweiler-Struthof was established at Kochendorf; the first 653 prisoners, selected from KZ Auschwitz-Birkenau and KZ Sachsenhausen, arrived on 3 September 1944. The camp held up to 1,800 prisoners. Underground production of turbines for the Heinkel AG and components for other firms including the Motorenwerke Mannheim AG and Siemens-Schuckertwerke began in early 1945. At least 213 prisoners died during camp operations; when the SS evacuated the camp at the end of March 1945, a further 213 or more died on a death march to KZ Dachau. In total, at least 447 prisoners lost their lives in connection with KZ Kochendorf. Salt extraction resumed in June 1945.

In the post-war decades, the mine was progressively modernised. In 1965, the operating company was restructured as the Südwestdeutsche Salinen GmbH; in 1968 it merged with the Vereinigte Badische Staatssalinen Dürrheim-Rappenau AG to become the Südwestdeutsche Salz AG, which in 1971 was reconstituted as the Südwestdeutsche Salzwerke AG, headquartered in Heilbronn. Annual output reached 900,000 tonnes in 1969. Plans to sink a second shaft were abandoned after the 1971 merger. To avoid the cost of a second shaft, the Kochendorf workings were linked underground to the Heilbronn salt mine in 1984, enabling shared access. Between 1986 and 1988 the Schacht König Wilhelm II. was extensively renovated and equipped with a new hoisting installation. In 1969 the surface salt-boiling plant at Jagstfeld was closed; salt evaporation thenceforth took place at the Kochendorf site itself.

In 1992, structural failures (Verbrüche) in the underground workings prompted a stability assessment. The assessment concluded that leaving the voids open would risk surface subsidence, and the Landesbergamt ordered the complete backfilling (Versatz) of the Grube Kochendorf. The last tonne of salt was extracted on 19 August 1994. Systematic backfilling of the voids began in 1996 and continued for many years, with the process eventually shifting to the Heilbronn mine sections via a new connecting roadway from 2012.

A visitor mine operated in the chambers adjacent to the König Wilhelm II. shaft from an early date; visitor underground access was suspended in the early 1970s and resumed in 1977, with annual visitor numbers rising to 140,000. The visitor mine was relaunched in a newly designed form on 1 May 2012, incorporating interactive displays, laser installations, a 40-metre slide, the Kristallsaal and Kuppelsaal chambers, and a Technikkammer with original mine machinery. The Gedenkstätte Ehemaliges KZ Kochendorf, a permanent memorial exhibition at 180 metres depth in a former salt chamber where prisoners worked, is integrated into the visitor circuit; the exhibition was first opened in 1996 and expanded in 1999. The Miklos-Klein-Stiftung, founded by the city of Bad Friedrichshall in 1999 and named after Miklos Klein, a Jewish Hungarian prisoner executed by the SS in October 1944, manages the memorial and is a founding member of the Verbund der Gedenkstätten im ehemaligen KZ-Komplex Natzweiler. In 2018 the network of Natzweiler sub-camp memorials received the European Cultural Heritage designation. The König Wilhelm II. headframe has stood above the shaft since 1899 and remains a landmark of the middle Neckar region. In 2020 it was decided to route part of the Suedlink high-voltage cable underground through the Kochendorf shaft and roadways over a distance of 16 kilometres.