The grotto of Santa Maria di Agnano opens on the slope of “monte” Risieddi, to the west of Ostuni, forming a large shelter under an overhang circa 10 m high. The cavity is almost horizontal as it goes back into the rock face, at between 169.50 and 173 m a.s.l.

The complex is divided into three sectors, the interior, the shelter under the overhang and the exterior.
The central part is dominated by the 17th century chapel which divides the great cavity into two areas, the west cavity and the east cavity.
In 1882 C. De Giorgi noted the existence of a ruined altar and the remains of a fresco in the west cavity. At the beginning of the 1970 D. Coppola focused attention on the archaeological importance of the complex of S. Maria di Agnano.

From the 21st April – 4th May 1987 D. Coppola, in collaboration with the Archaeological Superintendency for Apulia, dug a trial trench (8 × 3 m) which documented the existence of cult areas situated outside of the cavity itself, with the discovery of a 4th century B.C. hearth surrounded by votive offerings. Pottery fragments with dedicatory inscriptions and figured terracottas were also found. The first full excavation campaign in the grotto of Santa Maria di Agnano took place between the 16th September 1991-22nd February 1992.

The excavations uncovered very important palaeolithic evidence. In the west cavity two burials of the Gravettian period (Ostuni 1 and 2) were excavated, the individuals having been buried in a fetal position. Ostuni 1, dated to 24.410 ± 320 B.P. (Gif 9247) on the basis of the charcoal found in the grave, was a pregnant woman with the remains of a fetus at an advanced stage of development. The burial Ostuni 2 was later although still of the Gravettian culture and was recently dated from a bone fragment to 23450+ 170 B.P. (ETH-24006).

In the east cavity a 10 × 3 m trench was opened (divided into two sectors G, m 3 × 3 and E, m 7 × 3). The archaeological deposit reached a thickness of circa 3 m with stratified remains dating from from the medieval to Upper Palaeolithic periods. Outside the grotto the 2009 excavations documented the existence of an Epigravettian level (LTL2513A 17850 – 1770 cal BC.; LTL2786A 15255±65 -20.7±0.1 un-calibrated; LTL2514A 9700 – 9290 cal BC) followed by a collapse and an underlying Gravettian layer (LTL1811A 23945±110 -15.4±0.5), correlating with the burial Ostuni 1 in the interior. The extension of excavation in the external sanctuary area, with the collaboration of Martine Dewailly and Alessandro Quercia, exposed substantial remains of the Messapian sanctuary with in situ materials relating to cult rituals comprising local and imported pottery, Messapian inscriptions and bronzes. Numerous stone circles with votive pits and the remains of offerings, as well as the remains of a wall of squared limestone blocks were identified and will be excavated during 2010.