For the first 1,878 metres (6,161 ft) the river flows in an underground channel below the city of Bad Reichenhall.

After the route was determined in 1522, construction started in 1524 under the direction of master builder Fabian Zehentner and the supervision of the Salzmaier (supervisor of the saline) Hans Humbs.

At Kurstraße street, one of the shafts was renovated, and now through a glass plate one can see the Grabenbach flowing in the deep.

The river is passable by boat, and at irregular intervals guided tours through the tunnel are offered for small groups.

Additionally, there are pipes in the canal that carry the brine to the graduation tower and the spa pump room.