Frasassi Caves

Cool air meets you first. It is damp and still, and it smells faintly of wet stone. Outside, the summer heat of the Marche hills may be pressing on your shoulders. A few steps into the tunnel, that heat is gone. Your footsteps change too. They become softer, rounder, as if the rock itself is listening. Somewhere ahead, water drips onto stone in a slow, uneven rhythm. You are walking into the Frasassi Caves, one of the largest known cave systems in Italy.

Before we go deeper, picture where you came from. The caves sit in the limestone hills near the small town of Genga, in the province of Ancona. The Sentino river has cut a narrow gorge through these mountains, known as the Gola di Frasassi. Steep grey walls rise on both sides of the road. Woods of oak and hornbeam cling to the slopes. Above the river, the rock is full of holes, cracks and shelters. People have used caves in this gorge for a very long time.

Yet the great chambers you are about to see stayed unknown until quite recently. In 1971, a group of cave explorers from the speleological club of the Italian Alpine Club in Jesi was working in this area. According to the accounts of that discovery, they noticed a current of air coming from a narrow opening in the rock. Moving air in a cave often means there is a large empty space beyond. They followed it, and they lowered themselves into darkness.

What they found below was enormous. The first great chamber was named the Abisso Ancona, the Ancona Abyss, after the city of the explorers' home province. Guides like to say that Milan's cathedral could stand inside it with room to spare. Whether you take that literally or not, the scale is real. Your headlamp, or the tour lighting, cannot reach the far walls at once. The ceiling disappears into shadow high above your head.

Here is the first surprise. Most limestone caves form slowly, as rainwater soaks through the ground and dissolves the rock from above. Frasassi formed in a different way. Deep underground, water rich in hydrogen sulphide, the gas that smells of rotten eggs, rose up through the rock. When it met oxygen, it produced sulphuric acid. That acid ate through the limestone from below. Scientists study Frasassi as one of the clearest examples of this unusual process anywhere in the world.

That process is still going on in deeper parts of the system, far from the tourist path. In those flooded passages, researchers have found communities of microbes that live without sunlight. They draw their energy from sulphur chemistry instead. Some form soft, hanging strands that scientists informally call snottites, because of how they look. These life forms interest people who study how life might survive on other planets. So this quiet cave is also a working laboratory.

The section open to visitors is only a small part of the whole system. Explorers have mapped many kilometres of passages, and they continue to find more. The public route was opened in the 1970s. It follows walkways and steps through a sequence of halls. Visitors enter through an artificial tunnel, not through the narrow opening the explorers used. That tunnel was cut so that people could reach the chambers safely, without ropes or climbing gear.

Now look at the shapes around you. Every formation here grew from dripping water. Each drop carries a tiny amount of dissolved calcium carbonate. When the drop loses a little water and gas, it leaves a thin layer of mineral behind. Drops falling from the ceiling build stalactites downward. Drops landing on the floor build stalagmites upward. When the two finally meet, they form a single column. This growth is extremely slow, measured over thousands of years.

The guides have given names to many of the formations, and some of these names have become part of local tradition. You may hear about the Giants, a group of tall stalagmites near the start of the route. There is a broad sheet of pale flowstone that people call Niagara Falls, because it looks like water frozen in mid-fall. Elsewhere there are thin, pointed stalagmites known as the Candles. Try to spot them as your guide points them out.

Notice the colours as well. Much of the rock is creamy white, where the calcite is pure. In other places it turns honey, orange or rust. Those warmer tones usually come from small amounts of iron and other minerals carried by the water. Some surfaces still look wet and shine under the lights. Those formations are still active and still growing. Others are dry and dull, because water no longer reaches them. Life and pause, side by side.

Here is the second surprise. The temperature inside stays close to fourteen degrees Celsius through the whole year. Summer and winter make almost no difference down here. The humidity also stays very high. That is why the air feels heavy and why your clothes may feel slightly damp after an hour. It is also why visitors are asked not to touch the formations. Oils from human skin can stop the mineral from depositing, and a touched surface may stop growing.

When you return to daylight, the gorge still has more to offer. Not far from the caves, set inside a natural rock shelter, stands a small octagonal church in neoclassical style. It is known as the Temple of Valadier, after the Roman architect Giuseppe Valadier, and it dates from the nineteenth century. Near the entrance to the gorge, you can also find the Abbey of San Vittore alle Chiuse. It is a Romanesque church, a medieval style known for thick walls and round arches.

As you walk out, pause for a moment at the edge of the tunnel. Feel the warm air come back against your face. Listen to the river and the birds in the trees of the gorge. Behind you, in complete darkness, water is still dripping. It is adding another thin layer to stone that was already growing before anyone came here. And the cave will keep working long after the lights go out tonight.