Grotta degli Olmi

Grotta degli Olmi is a karst cave inside the Adelasia Nature Reserve, within the municipality of Cairo Montenotte in the province of Savona, in the Liguria region of Italy. Its entrance opens on the northern slope of the Ligurian Apennines at roughly 620 metres above sea level, making it one of the more notable caving sites in this stretch of the western Apennines and a draw for anyone interested in the region's mountain landscape and underground geology.

Where is Grotta degli Olmi and how do you get there?

The cave sits deep inside the Adelasia reserve, away from paved roads, so reaching it is part of the experience. The approach trail starts at around 400 metres above sea level and climbs through reserve terrain up to the cave mouth. Walking time is typically about an hour, through the kind of rugged, forested Apennine landscape shaped by the area's unusual bedrock.

What makes this cave stand out?

Grotta degli Olmi is unusually large for a cave in this part of Liguria: its passages add up to nearly 1,500 metres in total length, with a vertical range of about 135 metres between the highest and lowest points of the system. On account of this scale, it is sometimes described as the westernmost cave in the entire Apennine chain to exceed a kilometre in development. The surrounding rock is of particular interest to geologists, since it consists of ophiolites — rock of magmatic origin — which makes the site a useful reference point for studying the geological structure of the Ligurian Apennines.

What is inside the cave?

The system is not uniform throughout. Alongside dry upper passages, it has an active lower branch carrying an underground stream. That water resurfaces at a spot known locally as "Acqua che Bolle," from where it feeds into the local water supply. The presence of running water gives the lower sections a very different character from the dry galleries above — they are technically more demanding and call for real caving experience rather than casual exploration.

Local residents already knew of the cave and partly explored it in the early decades of the twentieth century, but systematic study only began in the 1960s, when a newly formed caving group, Gruppo Grotte Ferrania — later renamed Gruppo Speleologico Ferraniese — took up the work. It was during that period that the lateral passages and deeper sections, including the active lower branch, were discovered.

What kind of wildlife lives in the cave?

Explorations recorded the presence of a ground beetle, Sphodropsis ghilianii, a species adapted to cave life. Its discovery here pushed the known eastern boundary of the species' range further than previously documented, which makes Grotta degli Olmi a point of interest not only for cavers but also for biospeleologists and entomologists studying subterranean fauna.

Frequently asked questions

Where exactly is Grotta degli Olmi located? Inside the Adelasia Nature Reserve, in the municipality of Cairo Montenotte, province of Savona, Liguria, at an altitude of around 620 metres.

Can visitors explore it on their own? Reaching the entrance takes about an hour on a mountain trail, but going inside — especially into the sections with the active stream — requires caving equipment and experience. Visits are typically organized through caving groups, such as outings run by local CAI clubs.

How long is the cave? The passages total nearly 1,500 metres in length, with a vertical range of around 135 metres.

Why is the cave scientifically significant? It sits in an area of ophiolitic (magmatic) rock of interest to geologists, and it is home to the rare cave beetle Sphodropsis ghilianii, whose presence here extended the species' known eastern range.