Nuraghe Longu is located in the central area of Tertenia Marina, in the locality of Su Concali. It offers stunning views of the coastline. This nuraghe comprises a complex structure that follows the slope of the land, with the main tower at the highest point. The main tower is relatively small (measuring approximately 7.50 metres in diameter at its base and 8.60 metres in height). The small upper chamber has no staircase leading up from below and was probably reached from the rampart of the lower bastion. The ground-floor chamber contains a narrow niche and an opening in the rear wall communicating with the outside, both at floor level. A clearly visible stretch of the added bastion extends from the tower and immediately forms a smaller tower (whose chamber has lost its upper section and is filled with collapsed material).