Monte Tisiddu, Mountain summit in Ulassai, Italy.

Monte Tisiddu is a limestone tacco, a mesa-like mountain in the Ogliastra region of Sardinia, rising south of Ulassai. Its oval plateau covers almost two square kilometres, ringed by high rock walls that can be entered only at a few points along steep paths. The plateau is covered by dense evergreen Mediterranean forest dominated by holm oak, with deep hollows, and its highest point is Bruncu Matzeu at 957 metres.

The mountain formed millions of years ago from layers of limestone built up by ancient seas. Over time, erosion and weathering carved out the present-day cliffs and hollow spaces within the rock.

The mountain's name comes from the Sardinian word for the yew tree, which grows on its slopes. Shepherds from Ulassai have long used the plateau's evergreen holm oak forest for grazing, and the caves on the tacco, such as Grotta de ir Janas, carry names linked to local legends of the janas, the fairies of Sardinian folklore.

The hiking trails begin from different starting points around Ulassai and are marked with signs. It is wise to start early in the day and bring sturdy shoes and plenty of water.

Four named caves open in the tacco's flanks: Grotta Matzeu on the south side of Bruncu Matzeu, Grotta Basoccu on the western edge, Grotta s'Anterassas to the south and Grotta de ir Janas to the west. They are karst hollows dissolved in the dolomite, not carved by running water.