It was discovered by miners in around 1908, when perforating the tunnel called "La Isidra", whose entrance is through "El Prao Collao" of Celis. This is flanked by the heights of El Táladro and Pico Hugón and has the most marvellous views one can imagine. The coast of Asturians fans out from west to south, and the mountains of Sierra del Cuera, Peñamellera, el Naranjo de Bulnes and the Central Massif of the Picos de Europa can also be seen. Opposite are the hills of Hozalba and just behind them, Peñasagra, to the south-east of the Sierra del Cordel mountains and Pico Tres Mares.
The Sierra de Arnero range, which spans several thousands of hectares, is mostly formed by terrain covered by common forest land and meadows, which also belong to the townships, where hundreds of head of sheep, cattle and horses graze. No human intervention is visible, except for the ancient remains of the mines and some old shepherd huts. On both sides are tiny, well-kept villages with the traditional rural architecture of Cantabria. There are excellent communications, with connections to the dual carriageway of Cantabria, passing through Los Tánagos-Pesués, on the way to Puentenansa. Another road is now being built to connect El Soplao with the motorway at Roiz and Villanueva de Labarces.