The archaeological area is located near the edge of the plateau dug by the Rio d'Ottava, in Nurra, a region of northwestern Sardinia.
The complex includes an altar, a village and a hypogeic necropolis.
The altar is unique in its kind on the island and in the western Mediterranean. It consists of a large trunk-pyramidal terrace (m 36 x 29; height 5.40 m) and a long trapezoidal access ramp (length 41.80 m; width 7.00/13.50 m; height 9.00 m). The outer masonry consists of irregular rows of large, summarily sketched limestone blocks. The structure contains a layered filling of earth and stones.
The building is superimposed on a previous altar formed by a smaller quadrangular terrace (23.80 x 27.40 m; height 5.50 m) and a ramp (length 25 m; width 5.5 m).
On top of the terrace was the rectangular chapel (m 12.85 x m 7.20) plastered with ochre (the “red temple”), of which the floor and, in part, the perimeter wall (height 0.70 m) with an entrance lined with two holes are preserved; other holes, designed to contain the supporting beams of the double-sloped roof, are present in the floor of the compartment.
This first altar was built in an evolved phase of Ozieri culture (3200-2800 BC) in the center of a coeval inhabited by quadrangular huts, and above the remains of an older village of circular huts perhaps dating back to phases of the San Ciriaco culture (3400 BC).
Some elements connected with the sphere of the sacred are preserved from the village of Ozieri: an irregularly shaped table for trachyte offerings (m 2.80 x m 2.18) - close to the right side of the ramp - and a menhir (height 4.44 m) on the upper side, raised in recent years.
The burning of the altar, at the time of the Filigous culture (about 2800 BC), made it necessary to build a new structure, the one preserved today.
Perhaps a trapezoidal calcareous slab (m 3.15 x m 3.20) - located near the ramp - resting on three stone bases and equipped with seven holes at the edges and a natural swallow below: perhaps a table for bloody sacrifices, dates back to this phase.
Close to the slab, but foreign to the archaeological area, are two spheroidal calcareous stones of a sacred nature (circumference m 4.85; height m 0.90 - diam. m 0.60).
Three other limestone steles come from the building: one (inside the ramp), fragmentary (m 0.40 x m 0.36), has a lozenge and spirals; the second (N side of the terrace), 1.15 m high, shows a stylized female figure; the third (angle d. of the terrace), elliptical (m 0.28 x m 0.18), is marked by 13 parallel grooves crossed by at least two other perpendiculars.
The village huts that surround the altar and the ramp - dating back in part to the Abealzu phase (2600 BC) - have straight walls formed by a plinth of small stones on which a structure of raw bricks or plastered reeds and branches rested. Poles stuck in holes in the floor supported one or two sloping fringe roofs. The rooms have rectangular fireboxes, with a relief border, made of clay.
Among the excavated structures, the trapezoidal “sorcerer's hut” - located at the NE corner of the terrace - is particularly interesting, with 5 irregularly shaped rooms covered by a single-sloping roof; the hut owes its name to a tip of a bovine horn and to some bivalve shells found inside a jug.
The site was still visited at the time of the Monte Claro culture, the Campaniform Vase and Bonnanaro, and more sporadically, in the Nuragic, Phoenician-Punic, Roman and medieval ages.
The necropolis is carved into the limestone wall overlooking the course of the Ottava River, 500 m from the altar. It consists of eight multicellular hypogeums often decorated with bovine protomes and architectural elements.

History of excavations
The altar was excavated for the first time by Ercole Contu (1952-59); this was followed by the interventions of Santo Tinè (1979-90) and Alberto Moravetti (2000-01). A recent restoration has rebuilt half of the building.

Bibliography
E. Contu, “Megalithic Construction in Monte d'Accoddi”, in Journal of Prehistoric Sciences, VIII, 1953, pp. 199-202;
E. Contu, “Monte d'Accoddi (Sassari)”, in Encyclopedia of Ancient Classical and Oriental Art, V, Rome, Institute of the Italian Encyclopedia, 1963, pp. 166-167, figg. 237-238;
E. Contu, “Sassari Loc. Monte d'Accoddi”, in I Sardi: Sardinia from the Paleolithic to the Roman Age, edited by E. Anati, Milan, Jaca Book, 1984, pp. 296-297;
E. Contu, “Monte d'Accoddi-Sassari. Problems of studying and researching a unique prehistoric monument”, in The Deya conference of prehistory: early settlement in the western Mediterranean islands and the peripheral areas, Oxford, BAR, 1984, pp. 591-608;
S. Tinè, “New excavations in the sanctuary of Monte d'Accoddi (SS)”, in Annals of the Department of Studies of the Classical World and the Ancient Mediterranean, section of Archaeology and Ancient History, IX, 1987, pp. 9-22;
E. Contu, “Monte d'Accoddi (Sassari)”, in Proceedings of the Congress on the Age of Congress of copper in Europe ( Viareggio, 15-18 October 1987), 1988, pp. 536-537 (poster);
Monte d'Accoddi. 10 years of new excavations, by S. Tinè-A. Traverso, Genoa, Italian Institute of Experimental Archaeology, Archaeological Superintendence of Sassari and Nuoro, 1992, pp. 21-36, 97-98;
E. Contu, The prehistoric altar of Monte d'Accoddi. Sassari, C. Delfino, 2000 (Archaeological Sardinia. Guides and itineraries; 29);
A. Moravetti, The Terrace Altars of Monte d'Accoddi, “Darwin. Notebooks”, n. 1 (July-August 2006), pp. 6-19. 

How to get
on the former SS131 state road in the direction of Porto Torres, after crossing the junction for Platamona (at Km 222.3), the site is marked by tourist signs at the junction for Bancali. From here, turn left to enter the opposite lane and after 850 m turn right at the Strada Vicinale Monte d'Accoddi sign. The ticket office is located along the paved avenue, next to the car park.