The section of the Lahn below the town of Bad Laasphe is geographically known as the Upper Lahn Valley (German: Ober Lahntal).
Above Bad Laasphe, where the river flows between the Rothaargebirge on the left (i.e. to the north) and the Gladenbach Uplands on the right, the Lahn Valley is simply considered part of these mountains.

Between Niederlaasphe (of Bad Laasphe) and Wallau (of Biedenkopf), the river crosses the border between North-Rhine Westphalia and Hesse.
It then flows in an easterly direction through some districts of Biedenkopf (but not the central town) and the towns of Dautphetal and Lahntal.
It is joined from the right by the Perf at Wallau and at Friedensdorf (of Dautphetal) by the Dautphe (which flows in a side valley to the south).

Shortly after the village of Caldern (of Lahn Valley), the ridgeline of the Rothaargebirge on the north ends with the Wollenberg and that of the Gladenbach Bergland with the Hungert.
The Lahn leaves the Rhenish Slate Mountains for a long section and reaches the West Hesse Highlands, where it flows through the extreme south of the Wetschaft Depression, north of the Marburger Rücken.
Where the Wetschaft flows into it from the Burgwald forest in the north (near the Lahntal village of Göttingen), the Lahn immediately changes direction by 90° to the right.
The section of the Lahn below the town of Bad Laasphe is geographically known as the Upper Lahn Valley (German: Ober Lahntal). Above Bad Laasphe, where the river flows between the Rothaargebirge on the left (i.e. to the north) and the Gladenbach Uplands on the right, the Lahn Valley is simply considered part of these mountains.
Between Niederlaasphe (of Bad Laasphe) and Wallau (of Biedenkopf), the river crosses the border between North-Rhine Westphalia and Hesse. It then flows in an easterly direction through some districts of Biedenkopf (but not the central town) and the towns of Dautphetal and Lahntal. It is joined from the right by the Perf at Wallau and at Friedensdorf (of Dautphetal) by the Dautphe (which flows in a side valley to the south).
Shortly after the village of Caldern (of Lahn Valley), the ridgeline of the Rothaargebirge on the north ends with the Wollenberg and that of the Gladenbach Bergland with the Hungert. The Lahn leaves the Rhenish Slate Mountains for a long section and reaches the West Hesse Highlands, where it flows through the extreme south of the Wetschaft Depression, north of the Marburger Rücken. Where the Wetschaft flows into it from the Burgwald forest in the north (near the Lahntal village of Göttingen), the Lahn immediately changes direction by 90° to the right.
Lahn