The Northern Fryske Wâlden: the best-kept secret of Friesland. The combination of cultural history and nature has made the National Landscape of the Northern Fryske Wâlden one of the most unique regions in Europe. A region with its own history: clues are still visible, even after hundreds of years. Pingos from the ice age, boulder clay in the soil, peat formation, peat digs and small agricultural plots bordered by lines of trees including alder. The alder trees were planted to enclose cattle and to prevent the erosion of the sandy soil. They are now hugely important in maintaining the special biodiversity of the region. The local farmers are now largely responsible for the maintenance of this scenic landscape, which is probably the best-kept secret of Friesland.