The Cave of San Giovanni can be found in the municipality of Domusnovas, in the Iglesiente area (south-west Sardinia).
This cavern was carved by the waters of the Rio de Monte Narba (later Rio San Giovanni) in the oldest limestone rocks on the island belonging to the Lower Cambrian.
Its unusual feature comes from being mainly a natural tunnel. A road runs through it, previously accessible to cars, covering its entire length (850 metres). This aspect makes it unique in Italy and a rarity in the world. Indeed, there are only two similar examples in France and Australia.
The internal path extends in the north-south direction, with two monumental natural entrances. To the south, towards the town of Domusnovas, to the north on the Oridda Valley and the Marganai forest of oak trees.
Its naturalistic value, from a karstic point of view, comes from the presence of branches that are still active. The main branch, which can be followed along the road, features the flow of the river into large chambers, with different concretions like stalactite and stalagmite pools. As well as the main branch, the cave spreads across two levels, accessible only with speleology equipment, making the cave over 2 kilometres long.
The active branch “Su stampu de Pireddu” (given this name because it was thought to have been a hiding place of the bandit Pireddu) has a series of tunnels with small pools and siphons. Su Stampu is still to this day being studied and ends with a lake, a surface outcrop of a vast underground basin.
The “Bobore” branch, above the main tunnel, now fossil, has structures known as “karstic vacuums“.
The name stems from an old chapel dedicated to the saint and built in the Middle Ages in a natural niche of the cave. The chapel was demolished when the road was under construction and replaced by a small church of the same name, the church of San Giovanni, near the south entrance to the cavern.
Findings show that, in ancient times, the entrances to the cave were closed by fortified walls from the Nuragic age and of which only a few ruins have survived. Human presence from ancient times was proven by the discovery of a number of items, like pottery.
Since 1999, the cave has been known as a Natural monument and is environmentally protected.
