It ran through the northwestern Harz Foreland from Börßum via Salzgitter, Ringelheim and Seesen to Kreiensen.

The Brunswick–Hanover Treaty of 1837 that regulated the construction of the Brunswick–Bad Harzburg railway had already established a basic agreement allowing both countries to work together towards a southern link.

Three months earlier the Hanoverian Southern Railway was opened from Hanover to Kassel.

The line was successful and in 1865, the Altenbeken–Kreiensen railway was opened, creating a western connection with the Ruhr area.

This connection became an important east–west route, with traffic to and from Göttingen and Frankfurt stronger than that to and from the Ruhr.