The Frasassi Caves of Italy are a cavernous system ithat stretches beneath the Appennine Mountains for 13km (8mi).

They lie in La Gola di Frasassi, or Frasassi Gorge, in the Italian province of Ancona.

The Frasassi Caves were discovered in 1971 by members of the Marchigiani speleological group of Ancona.

Frasassi Gorge, which winds for almost 3km (2mi) between steep walls of rock, was carved by the tumbling waters of the River Sentino, a tributary of the Esino. At its southern end stands the village of San Vittore del Chiuse, renowned for the therapeutic qualities of its sulfurous springs. The limestone walls of the gorge are marked by numerous cave openings. One of these caves, II Sanctuaria della Grotta, "the Sanctuary Cave", contains an octagonal church erected by Pope Leo XII in 1828 and an 11th-century chapel dedicated to a local saint, Santa Maria del Frasassi.

The cave is full of stalagmites and stalactites, which create scenes of giant "marble pillars, crystalline inflorescences, delicate curtains of frosted rock and huge vaults lined with fragile yet razor-sharp spikes.

The largest cave system in Frasassi's complex is La Grotta Grande del Vento, "the Great Wind Cave". Public access to this subterranean wonderland leads along a smooth walkway that runs for 1.6km (1mi) into the limestone hills. A short tunnel, bored through the rock to make entrance easier, opens into a cathedral-sized chamber.

In this cave's centre a shaft, named the Ancona Abyss in honor of the men who discovered the caves, plunges down to unfathomable depths. Close to the hole stands II Gigante, "the Giant", an enormous column with ribbed and convoluted sides. Facing the Giant stands the cascading sheet of rock known as La Cascata del Niagara, "the Niagara Falls", a familiar feature of other limestone caves, such as those beneath Cheddar Gorge in England.

Deeper still lies La Sala delle Candeline, "the Room of Candles", where an array of short, upright stalagmites emerges from shallow water. White in color and encircled at the base by a small "cup", the majesty of these pillars is further enhanced by imaginative lighting. Illumination also brings out the best from the Grand Canyon formation where as much consideration has been given to shadows as to light. Black areas emphasize cavities and gullies, while bright lights pinpoint the delicate colors of the bands that mark the thin curtains of rock.

Formation of the Frasassi Caves

The limestone hills in the Frasassi region of the Appennine Mountains, like those of Guilin in China, are an example of a karst landscape, the term geologists use to describe terrain modeled by acidic rainwater.

As rain falls, it absorbs a small amount of carbon dioxide gas from the air. This turns the rain into a dilute solution of carbonic acid that dissolves calcium carbonate, the principal constituent of limestone.

When, around one million years ago, the River Sentino began to carve out the Frasassi Gorge, rainwater trickled and seeped through tiny fractures in the limestone, and gradually widened them. Where the water encountered horizontal fractures, it formed underground streams and excavated long tunnels with connecting caverns.

At Frasassi, the acidic water percolated from above and met the underlying water table at the level where the Great Wind Cave now lies. Unable to penetrate deeper, the water spread sideways and fashioned the labyrinthine grotto.

Since their formation, the caves have been all but emptied by a drop of almost 300m (1,000ft) in the region's water table. Once this had occurred, stalagmites and stalactites started to form as the water returned to the rocks the calcium carbonate it had earlier removed. Water saturated with this mineral dripped from chamber roofs and cave ceilings to the floors below. Water drops that hung for a few moments before falling were diminished by evaporation, leaving behind minute grains of calcium carbonate, or travertine.

Over the centuries, the travertine grew gradually downward to form enormous stalactites.

Dripping water, which deposited travertine when it reached the floor, formed stalagmites, as in the Room of Candles. In some chambers, such as La Sala dell' Infinito, "the Room of the Infinite", the stalagmites and stalactites have joined, creating a number of fluted pillars that link the floor to the ceiling.

Life in the Frasassi Caves

Plants and animals have become adapted to life in the Frasassi caves. There is high humidity and a constant temperature of 13°C (55°F), which many organisms find beneficial. However, they most also contend with total darkness and a scarce supply of food. Nevertheless, blind cave salamanders, crayfish, millipedes and flatworms are able to flourish in these conditions. The most prolific inhabitants are bats, which roost in La Grotta del Nottole, "the Cave of the Bats", during the day and emerge at night to feed.