From east to west, the Nature Trail traverses the Cantabrian Mountains that stretch across inland Asturias on a journey that leaves no traveller indifferent. The extraordinary beauty of the natural environment of these spectacular mountain counties will not only amaze the visitor, but also provide a better understanding of the rural customs and traditional farming practices that still today continue to be the way of life in many manors and villages.
The route, divided into 27 sections of varying difficulty, runs just over 600 km, of which about 111 km are alternative itineraries to the main route. The route runs along the rugged, fragmented and mountainous terrain of Asturias, where the topography and climate have shaped its natural wealth and the different forms and systems used by humans to tap natural resources. The remarkable diversity of landscapes of the Principality is a result of this interaction.
The Cantabrian Mountains Nature Trail starts in Peñamellera Baja County, near Cantabria, and ends in Santa Eulalia de Oscos County, which almost borders Galicia. Along its entire length, the trail winds through the counties of Cabrales, Onís, Cangas de Onís, Parres, Piloña, Nava, Bimenes, Laviana, Alles, Lena, Quirós, Santo Adriano, Proaza, Yernes y Tameza, Teverga, Belmonte de Miranda, Tineo, Cangas del Narcea, Allande and Grandas de Salime, passing through a variety of spectacular landscapes, from peaks and grazing lands in the high mountain pastures, to the vast meadows and pasture lands that carpet the numerous valleys that form the backbone of the region.
Thus, the Nature Trail stretches across some of the most unique protected nature sites like Sierra de Cuera Protected Landscape near the Picos de Europa National Park, the Redes Nature Park, Cuencas Mineras Protected Landscape, in the central area, Pico Caldoveiro Protected Landscape, the Las Ubiñas-La Mesa Nature Park, and Sierras de Carondio y Valledor Protected Landscape in western Asturias. The route ventures into oak forests in the east, and oak and beech forests in the west, as well as belts of chestnuts and conifer forests in between and winds through riparian forests along the various rivers that it crosses.
The route runs first through a floodplain then climbs up the valley formed by the River Cares and its tributaries, to continue across the plains of the rivers Sella and Piloña. As it winds between Benya and Cangas de Onís, the route overlooks the Güeña River Valley, and from Sierra del Sellón, the La Marea valley. It then crosses Sierra de Peñamayor towards the Nalón Valley. The valleys of Villoria and Aller, which connect with the Negro River Valley through the Coto Beyo range, can be seen in the distance from the Peña Mea massif. In the municipality of Lena, the route descends to Campomanes, where the valleys of Huerna and Caudal Pajares meet. At Quirós, the Trail approaches the Teso River near the village of El Valle.
The Nature Trail runs along the River Trubia in the section known as the Bear Trail. Further on in Belmonte de Miranda, it heads down into the Pigüeña River Valley in search of the River Narcea, of which it is the main tributary. In the land of cattle herders, the Trail approaches the town of Tuña, in the Genestaza River Valley, and then crosses the River Narcea near Corias. In the later sections, the route climbs down to the Irondo River Valley to arrive at Besullo, then continues up the Pomar River Valley to descend again to the banks of the River Oro and Salime Reservoir. In its final stretch, the route passes close to the rivers Navía and Eo.
Throughout this route, the Nature Trail crosses over several ancient medieval bridges and approaches little known places and villages that tell of its rich historical and cultural heritage. It still preserves the traditional architecture of "hórreos", manors, chapels, churches, towers and stately palaces, among other buildings, many of which have been converted into interesting museums of local customs, festivals and traditions rooted in the Asturian geography. Thus, the Trail overlaps in some sections with historic trails, such as the Carisa Roman road, the Camín Real de La Mesa or the French Route of the Original Way of St. James. For those interested in trekking, the route is also peppered with Celts, Roman and medieval archaeological sites.