Active salt mine ventilation shaft at Heidwinkel near Grasleben, sunk in 1937–1939 as a dedicated access shaft for the Heeresmunitionsanstalt Grasleben, now serving as the location of the Hauptgrubenlüfter for the Steinsalzwerk Braunschweig-Lüneburg, with
Schacht Heidwinkel II is the second and younger of the two shaft installations at Heidwinkel, a settlement approximately two kilometres north-west of Grasleben in the Landkreis Helmstedt, Niedersachsen. The Heidwinkel I shaft had been sunk from April 1912 by the Gewerkschaft Braunschweig-Lüneburg and commenced potash production on 1 November 1913; raw salt was transported by aerial ropeway, then narrow-gauge railway, to the processing plant at Grasleben. In 1936 the Wehrmacht assumed control of the Heidwinkel shaft installation to create the Heeresmunitionsanstalt (Bergwerk) Grasleben.
Because the existing Schacht Heidwinkel I remained in civil use and the military required an independent access point, a new shaft — Schacht Heidwinkel II — was sunk between 1937 and 1939 to a depth of 662 metres. In 1941 a winding installation and a steel headframe were erected. Seventy-two underground storage chambers on two levels were fitted out for munitions.
Surface facilities included a munitions manufacturing compound west of the shaft and a workers' settlement of four apartment buildings to the east; approximately one kilometre to the west the Waldlager Heidwinkel provided accommodation for additional forced labour. Operations as a Heeresmunitionsanstalt began in 1938. In April 1945 US Army forces occupied the Heidwinkel installation.
In 1949, after full Allied munitions clearance, the Schachtanlage Heidwinkel I/II was returned to the Gewerkschaft Braunschweig-Lüneburg and salt hoisting resumed. An underground connection between the Heidwinkel shafts and the Grasleben shaft was established for the first time in July 1957. Today, the Schacht Heidwinkel II — also designated Schacht Grasleben III — is the site of the Hauptgrubenlüfter for the combined mine, which serves as the principal ventilation intake for the Steinsalzwerk Braunschweig-Lüneburg.
Two further levels at 570 and 645 metres, originally the Muna levels, remain part of the mine infrastructure. The shaft has a Notbefahrungseinrichtung (emergency access installation) but does not hoist salt. Its steel headframe and Fördermaschinenhaus survive.
The history of Schacht Heidwinkel II is inseparable from the decision of the Wehrmacht in 1936 to convert the existing Kali- und Steinsalzwerk Braunschweig-Lüneburg installation at Heidwinkel into an underground munitions facility. The older Schacht Heidwinkel I — sunk in only fourteen months from April 1912, 670 metres deep and 4.75 metres in internal diameter — had commenced potash production on 1 November 1913. It used cast-iron tubbing to 92 metres and masonry below. Raw salt was transported first by aerial ropeway and later by narrow-gauge railway to the processing plant at the Grasleben shaft. Both Heidwinkel and Grasleben initially remained legally independent Bergwerke because the Braunschweig mining law did not require a mandatory second shaft for each concession; the two installations were consequently not connected underground until 1957.
In 1936 the Wehrmacht's economic planning authorities identified the Heidwinkel underground workings as suitable for protected munitions storage. They took over the Schacht Heidwinkel I site and simultaneously recognised the need for an independent shaft that would allow the Heeresmunitionsanstalt to function separately from the civil salt-hoisting operation. Between 1937 and 1939, Schacht Heidwinkel II was sunk to 662 metres. In 1941 a winding installation and a steel Fördergerüst were erected above it. On two underground levels — the original Muna levels at 570 and 645 metres — seventy-two munitions storage chambers were fitted out. The Heeresmunitionsanstalt began operations in 1938. Surface facilities included a munitions manufacturing compound (Munitionsfertigungsgelände) west of Schacht I, a residential compound of four apartment buildings for permanent Muna workers east of the shaft, and approximately one kilometre west the Waldlager Heidwinkel labour camp, which housed additional workers. Towards the end of the war the underground workings were also used briefly for the storage of cultural objects before hostilities reached the area.
In April 1945 US Army combat troops occupied the Heidwinkel installation; it was subsequently transferred to British Army administration. From 1946, displaced persons (Heimatvertriebene) from Germany's eastern territories settled in the former camp buildings. In 1946 a Catholic chapel was established in the Waldlager compound. In 1949, after all munitions chambers had been cleared and sealed, the Allied military returned the Schachtanlage Heidwinkel I/II to the Gewerkschaft Braunschweig-Lüneburg, which resumed salt hoisting the same year.
In July 1957 an underground connection of 2,500 metres was driven for the first time between the Heidwinkel I/II installation and the Schacht Grasleben, linking what had previously been legally independent workings into a single operation. The two former Muna levels at 570 and 645 metres were retained as working levels of the mine infrastructure. The Schacht Heidwinkel II — known in current mine terminology also as Schacht Grasleben III — is today the location of the underground Hauptgrubenlüfter (main ventilation fan) for the Steinsalzwerk Braunschweig-Lüneburg. Both Heidwinkel shafts serve as the second shaft entrance to the combined mine; neither currently hoists salt. Schacht Heidwinkel I has its Fördergerüst, Fördermaschinenhaus, and Schachthalle; Schacht Heidwinkel II has its Fördergerüst and Fördermaschinenhaus, together with a Notbefahrungseinrichtung. Since 2002 the Steinsalzwerk Braunschweig-Lüneburg, including both Heidwinkel shafts, belongs to the European Salt Company (ESCO), a wholly owned subsidiary of K+S.