Spiaggia di Su Tiriarzu, Sandy beach in Posada, Sardinia, Italy

Su Tiriarzu is a beach of coarse sand in the municipality of Posada, stretching about 1.6 km, the longest of the town's five beaches. It begins north of the mouth of the Longu pond, and the water deepens quickly a few metres from the shore. Access is only via two bridges, one over the Longu outlet and one over the Rio Santa Caterina.

The coast near Posada has been a place of trade and sea routes since ancient times. Centuries of connection to Mediterranean shipping shaped how the settlement developed and its bond with the sea.

Su Tiriarzu is known for kitesurfing: its exposure makes it one of the five Posada beaches, alongside San Giovanni, Iscraios, Due Pini and Orvile, awarded the Legambiente 5 Vele for ten years. A kitesurf school operates here, and kayak or canoe trips leave from the beach into the open sea or up the Longu pond, the Rio Santa Caterina and the Rio Posada.

The beach is a short walk from nearby parking and has shower facilities available for visitors. It is best visited outside peak summer months, when the shore is quieter and the water remains warm.

Access to the beach is only possible via two bridges: one over the mouth of the Longu pond at the southern end, and one further north over the Rio Santa Caterina linking the car park to the sand. The 1.6 km shoreline, the longest of Posada's five beaches, is preceded by these two watercourses.