Beneath our feet: exploring the most fascinating caves between Trieste and Slovenia

There is a moment when the step becomes uncertain, the light goes out, and we remain listening. Entering one of the karst caves in Slovenia is always a small rite of passage: we leave the surface world to enter another world made of rock, water, darkness and… sound. Yes, because in caves you listen differently. Sounds are amplified, or they disappear. Echoes, drops, breaths. And so, on our walking tours between Trieste, Slovenia and Croatia, we like to take our guests underground from time to time, exploring some of the most beautiful caves in the Slovenian Karst.

The Karst, which we have known and walked through for years, is a land full of caves. Some are famous and equipped, others are more hidden and silent. Either way, they are true “natural cathedrals”, where every step is like a deep thought.

A land shaped by water and time

Karst – the rocky area that covers Trieste, western Slovenia and part of Istria – is named after this type of landscape. “Kras” in Slovenian means stony ground, and it gave rise to the term “karst,” which is used throughout the world to refer to those areas formed by water disappearing, burrowing, reemerging, and creating underground cavities such as the karst caves in Slovenia, known worldwide for their beauty and geological importance.

It is a world of sinkholes, swallow holes, resurgences and caves. It is also a deeply cultural world: for centuries the inhabitants of the Karst have lived with these mysterious cavities, exploring them, telling stories about them, fearing and celebrating them.

Karst caves in Slovenia and Trieste you shouldn’t miss

• Grotta Gigante (Italy): located just minutes from Trieste, this is one of the largest natural caves in the world that can be visited on foot. Its impressive size and dramatic lighting make it a fascinating destination.
• The Škocjan Caves / Škocjanske jame (Slovenia): a UNESCO World Heritage Site, spectacular for the underground canyon carved by the Reka River. Here, the power of the water became an architect, shaping towering halls and dizzying tunnels.
• Postojna Caves (Slovenia): famous for the tourist train that takes visitors deep underground, and for the incredible complex of galleries, stalactites and stalagmites. An underground world that can be easily explored even with small children.
• Vilenica Cave (Slovenia): considered the oldest tourist cave in the world (open to the public since the 17th century), it is also a place of poetry. Every year, the Vilenica International Literary Prize is awarded in one of its underground halls. The name recalls the vilenica, the fairies of Slovenian tradition.
• Križna jama (Slovenia) – One of the most authentic Slovenian caves, famous for its underground lakes. It is visited in small groups with lamps, paddling silently in small boats. It is a rare and intimate experience.
• The caves of the Trieste Karst: In addition to the caves equipped for tourism, there are dozens of smaller caves that can only be visited with an expert guide. Some of them are natural, others were used during the First World War as shelters, hospitals, depots. The underground preserves traces of forgotten history.

When cinema goes underground

Caves have inspired movies, books, documentaries. Spaces that evoke mystery, transformation, testing. In The Descent, darkness becomes suspense; in Journey to the Center of the Earth, it becomes wonder. Even the Postojna Caves have been used as movie sets, as in the film Armor of God with Jackie Chan.

But it is mostly the sound that tells the story of the depths: the muffled silence, the voices that stretch out, the drops that ring like bells. Cinema has captured all this and turned it into a sensory experience for the viewer.

Some concrete examples are:

• Waitomo Caves (New Zealand): used to film scenes in the Lord of the Rings saga. These caves, famous for the presence of bioluminescent fireflies, added a mystical atmosphere to the Middle-earth locations.
• The Ajanta Caves (India): used as an inspiration for Indiana Jones and the Temple of Doom (1984). The movie features caves full of underground temples based on real Indian religious complexes.
• Postojna Caves (Slovenia): these caves, among the most famous in Europe, have been used as locations for several films because of their vastness and the spectacular limestone formations. One of the most famous productions to have used this setting is Armour of God (1986), an action film starring Jackie Chan, which includes scenes shot inside the spectacular cave halls. Historical films and documentaries have also used Postojna Cave to recreate mysterious and fascinating settings.
• Mammoth Caverns (USA): used in documentaries and films such as The Descent (2005), a horror film that uses the darkness and isolation of caves to create suspense.

In addition to movies, caves are also featured in video games and TV series. For example, The Witcher and Game of Thrones use caves as evocative settings for key plot moments.

Walking underground: another way to explore

Our travels are often outdoors, through forests, mountains and lands. But every now and then we like to go down. To explore a cave is to explore ourselves: to step out of our comfort zone, to listen with different senses, to perceive time differently. Exploring the karst caves in Slovenia on foot means immersing yourself in silence, sound, and timeless beauty.

There are caves that look like theaters, others that resemble temples, still others that hold ancient legends and stories. To visit them on foot, slowly, with a guide who knows them, means to get in tune with the stone, with the water, with the darkness. And to come out a little different.

The world’s most spectacular caves

If the Karst between Trieste and Slovenia is a veritable underground treasure trove, there are caves around the world so vast, deep or fascinating that they seem like places out of a fantasy novel. Some are easy to visit, others are reserved for a few experienced cavers, but all tell of the grandeur and wonder hidden beneath the earth’s surface.

• Mammoth Cave (United States) – Located in Kentucky, it is the longest cave in the world, with more than 680 kilometers of explored tunnels. Its name is not related to prehistoric fossils, but to the truly “mammoth” size of the system. Some sections are open to the public and can be explored on foot with national park guides.
• Sơn Đoòng (Vietnam) – Only discovered in 2009, it is now considered the largest natural cave in the world by volume. Up to 200 meters high and more than 150 meters wide, inside are jungles, rivers and even clouds! Located in the Phong Nha-Kẻ Bàng National Park, it can only be visited by selected small groups with special permits.
• Lechuguilla Cave (USA) – Hidden beneath the New Mexico desert, it is one of the deepest and most spectacular caves in North America. It is famous for its rare crystal formations and the scientific research conducted in its unique environment. It is not open to tourism, but continues to inspire scientists and enthusiasts.
• Eisriesenwelt Cave (Austria) – Located near Salzburg, the Eisriesenwelt Cave is the largest glacial cave in the world. Inside, even in midsummer, you can walk among columns and ice sculptures created by nature. It is a cold but fascinating experience.
• Fingal Cave (Scotland) – A basalt temple overlooking the sea on the island of Staffa. It has no great halls, but it amazes with its perfect hexagonal columns, similar to those of the Giant’s Causeway in Ireland. Its acoustics also inspired Mendelssohn to compose the Hebrides Overture here.
• Waitomo Caves (Nuova Zelanda) – A magical place where thousands of bioluminescent glowworms illuminate the darkness like an underground starry sky. Navigating in silence on a boat among the blue lights is an almost mystical experience.
• Marble Cathedral (Cile) – In the heart of Chilean Patagonia, on the turquoise waters of Lago General Carrera, are these incredible caverns carved out of marble rock. They are visited by boat, amidst dazzling reflections and natural columns.

From ice to marble, jungle to basalt, the world’s caves are many, varied, and extraordinary. Some require a sense of adventure, others are within easy reach. But all have a story to tell. There really is something for everyone: all you have to do is choose which way to go.

These underground wonders also remind us that planet Earth is made up of layers, depths, surprises. And that, as is often the case, the greatest beauties are not always in the spotlight: you have to walk, look, listen.

Why talk about it in a walking blog?

Because many of our walking routes pass through natural caves, karst cavities, or small, hidden underground passages. And every time we enter one of these spaces, we find ourselves in a different world—one where the senses adapt and the pace of perception changes.

Writing about caves means enriching the way we walk. It means recognizing that not all landscapes are visible at first glance. Some must be listened to. Others must be entered slowly, with respect and curiosity.

How many times have we paused, amazed, just to hear our own voice echo off the stone walls? Or to feel the thick silence wrap around us like a second skin?

For those who love walking, caves are not a detour: they’re a dimension of the journey. They invite us to step out of the everyday and into something deeper—literally and metaphorically.

We are waiting for you, between light and shadow, to walk with us in the heart of the earth.

PHOTO: www.slovenia.info – Jošt Gantar; Nea Culpa d.o.o.; Jaka Ceglar; Društvo ljubiteljev Križne jame, arhiv RRA Zeleni kras d.o.o.