Different geological folds and glaciations have shaped a tortuous landscape sculpted by ice and the effect of water on the limestone, forming a magnificent karst mountain system. The three main massifs of this natural wonder are bounded by deep valleys and gorges, which arose due to the erosive passage of the sharp tongues of glacial ice and the force of the rivers' waters which, even today, continue to dissolve the limestone, shaping the rock at its whim. Both the River Deva and the Dobra, a tributary of the Sella, flank the mountains to the west and east of this mountain chain, with the River Cares and its tributary, the Duje, being responsible for dividing up the park into its three massifs.
The central massif is home to the highest peaks in the Cantabrian Mountains in the form of the sheer-sided Urrieles, dominated by the most emblematic reference in the Picos de Europa: the immense beauty of Naranjo de Bulnes or Urriellu Peak. Its 2,519 metres of difficult terrain have not prevented human settlements from emerging, the most famous being the village of Bulnes. Until 2001, it was accessible only via a steep, narrow mountain path. Since then, access to the village is easier thanks to the funicular railway that cuts across the mountain from the town of Poncebos.
To the east of the Urrieles lies the eastern massif, the Andara, the smallest with a gentler profile, whose highest peak is Morra Lechugales at 2,400 metres. The westernmost of the three massifs is that of the Picos de Cornión, near the Royal Site of Covadonga, a place of pilgrimage visited by thousands of people each year. There Lakes Enol and Ercina reflect the high mountains where the legendary history of Asturias was forged.
Visitors to the grotto itself in Covadonga can enjoy the ever-present footprint of the karst process in the Picos, in the picturesque emergence of the Orandi River below the image of the Virgin. Between the Urrieles and the Cornión and separating the central and western massifs from south to north, runs the River Cares, whose crystalline waters rage throughout its course. Outstanding among the beautiful peaks of the western massif rises La Peña Santa de Castilla at 2,596 metres. On the way to this peak can be found Ordiales Scenic Balcony, with a drop of almost 1,000 metres down to the valley below, instilling awe in all who visit it.