Frog Route

Nature Reserve "Upper Treene Landscape": The last ice age created the Fröruper Mountains about 12,000 years ago. This end moraine landscape is a mosaic of different habitats. Various forest types alternate with smaller moors and heath areas. Additionally, gravel mining at the beginning of the last century shaped the appearance of the Fröruper Mountains.
A very special nature reserve is the Upper Treene Landscape, characterized by a small-scale mosaic of species-rich habitats consisting of inland dunes, raised bogs, wooded hills, wide valley areas, lakes, and flowing waters. The Treene, which springs from the Treßsee and flows mostly unregulated through the area, gives the region its name. A traditional shepherding flock with specially trained herding dogs makes an active contribution to the near-natural landscape management in the region.

The Ihlseestrom Lowland: The Ihlseestrom Lowland is a spacious wetland formed from the silting up of a meltwater channel from the last ice age, surrounded by moraine ridges. A particularly beautiful view of this area is offered by a viewing platform, which can be reached via a small hiking trail from the old gravel pit.

Gravel Mining: Around 1920, the largest gravel plant in the north was located in what is now the recreational area. Stones for coastal protection and for constructing the land connection to the island of Sylt ("Hindenburgdam") were mined here.
The forest area around the gravel pit, cleared after the war, was temporarily used for agriculture and reforested from 1950. In 1970, the district of Schleswig-Flensburg set up a recreational facility with parking, playground, and barbecue areas. Since 1998, the area has been owned by the Kurt and Erika Schrobach Foundation.

The Treene: The Treene is one of the most beautiful rivers in Schleswig-Holstein and part of the largest contiguous river area – the Eider-Treene-Sorge region. The Treene springs from the Treßsee, located south of Flensburg. Its source rivers Kielstau and Bondenau drain wide parts of the Angeln landscape. The upper river course is natural, and the banks provide undisturbed protection for plants and animals. In Frörup on the edge of the Upper Treene Landscape, the Treene drives a watermill probably dating back to the 13th century.