At one time, it may have been a meeting place for Nuragic populations and then, according to popular legends, it became the entrance to the Underworld. It emerges from the earth like a gigantic finger stretched towards the sky and is a reference point, visible from a great distance, for hikers in a wild territory. Perda ‘e Liana is an extraordinary rocky formation declared a natural monument in 1993. The unusual ‘mount’, known as taccu or tonneri in Sardinian, stands out in the territory of Gairo Sant’Elena: it is the greatest piece of evidence of the erosive action of the weather, which lasted tens of millions of years, on an extensive limestone covering in the Ogliastra area on the border with Barbagia of Seulo. The erosion progressively isolated the ‘tower’ and shaped its base. It is the highest (1293 metres) of the numerous buttes in Ogliastra, northern extremity of the plateau of Tonneri, about two kilometres away, which connects with the saddle of s’Arcu ‘e su Pirastu Trottu. In the distant past, they may have formed a single mountain ridge.