Go Inside These World-Famous, Rarely Seen River Caves

See stunning photos of these strictly protected underground caves in Slovenia.

Slovenia is a world-famous caving destination, with around 8,000 jamas, or caves, located in a country that’s smaller than Vermont. Of those 8,000 caves, however, only around 20 are considered “show caves”—caves that contain a unique beauty and scale that rivals many of the much larger karstic topographies found in southeastern China, Vietnam, Laos, and Papua New Guinea.

A number of powerful rivers traverse Slovenia, mostly overland, but at a few unique locations the rivers will mysteriously disappear into the ground, down into a hidden filigree of subterranean conduits bore through the porous, cavernous limestone.

Robbie Shone, a photographer and caver originally from the U.K. but now living in Austria, has been working to photograph underground points in Slovenia where several of its most famous rivers—namely, the Reka, Rak, and Pivka rivers—either disappear or emerge.

“The Reka river is the key to this whole project,” says Shone, who dreamed of capturing these images for the past decade. “It strings together the entire story.”

KAC?NA JAMA: Shone had been wanting this shot for 10 years—ever since he first saw a similar photo on the internet of this cave, Kac?na jama. Kac?na’s dual skylights are clearly the cave’s most striking feature, but what’s not obvious from the picture is the sheer scale of this chamber.

The entrance is actually over 76m above the skylights, and it’s another 76m down to the underground river below, making for a total of 152m of free-hanging descent from rim to the cavern floor. Getting back out would take an experienced caver about 45 minutes to ascend the ropes using mechanical ascenders, a physically gruelling and airy proposition no matter how fit you are. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

SLOVENIA'S SECRET RIVERS

Beneath the village of Škocjan lie its namesake caves, a UNESCO heritage site, into which an entire river is seemingly swallowed whole by the earth. The Reka River—reka means river in Slovene; hence the Reka Reka—plunges abruptly into a syphon in the rock, yet it continues flowing along a winding, underground channel before ultimately re-emerging 39km later near Monfalcone, Italy. Here, it briefly joins the Timavo River and a kilometre later dumps into the Adriatic Sea.

“River caves are not necessarily rare. You can find them all over the world,” explains Katarina Kosic Ficco, a Slovenian caver and one of the four team members on Shone’s expedition. She is also a PhD candidate in karstology at the University of Nova Gorica, Slovenia, through the Karst Research Institute. “However, there are only a few karst landscapes where the river caves reach such extensive sizes as in Slovenia.”

POSTOJNA JAMA: While Postojna is the most heavily touristed cave in Slovenia, Shone and his team gained permission to visit locations off the beaten path. Here, in a spot deeper in the cave, one of Shone’s assistants swims while holding a single-use magnesium flash bulb that emits five times the light output as a standard battery-operated camera strobe—power that’s needed to showcase the emerald-green colour of the pool. Shone says his decision to include figures in his cave landscapes adds a sense of scale for the viewer, while here it also has the benefit of blocking the blinding, white flash bulb. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

The Karst Plateau is a geographic region of southwestern Slovenia that stretches from the coast of the Adriatic Sea in the south up to the Vipava Valley, a corridor of the Slovenian Littoral that enters northeastern Italy along a contiguous bedrock of limestone.

Beneath the kras—meaning rock or barren ground in Slovene—lies a complex subterranean world, formed by the limestone’s chemical dissolution over eons. The derivative English term karst typically refers to a landscape shaped by rock susceptible to dissolution. Karstology, the scholarly study of this geological and hydrological phenomenon, was originally pioneered here in Slovenia.

“The main part of caving I love is that you are exploring the unknown and that you are always learning about its development,” says Kosic Ficco. “From a non-scientific perspective, river caves are amazing because they enable the visitor to go canyoning underground, to float the lakes and giant rivers where the sun doesn't shine, observe the amazing power of water in action and aquatic cave animals in their natural environment, and enjoy the beauties of speleothems at the same time.”

ŠKOCJAN JAMA: The voluminous Škocjan jama is a UNESCO natural and cultural heritage site recognized for its exceptional significance. As such, it’s also one of Slovenia’s most popular show caves, with a carved gangway that leads tourists to the point where the Reka Reka plunges underground only to re-emerge 39km later in Italy. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

CAVES WITH A PURPOSE

A fusion of Slovene and Italian communities exist along the karst, which yields a terroir conducive to the native Teran grape. The succeeding red wine is best drunk within the first year of fermentation, however, as the high concentration of iron in the fruit doesn’t age well. The wine may very well pair best with a slice of pršut, a regional rendition of prosciutto that’s been dried over many months in the bora winds.

The caves themselves have played many roles throughout history. People have used them as a water resource, a refrigerator, and even storage for munition during war. Throughout the Ice Ages, Križna jama was a vital shelter for bears—some 2,000 bear skeletons remain. Today, river caves are important habitats for many animal species, several of them endangered.

POSTOJNA JAMA: Shone and his team explored these caves when the water was quite low. During winter floods, the rivers swell. You can see the flood line well above the two figures traversing a steel-cable via ferrata that’s located deep in Postojna, the second-longest cave system in Slovenia at 24,340m. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

The Postojna jama is Slovenia’s largest and most touristed cave, complete with a train that hauls visitors through labyrinthine tunnels and halls replete with fossils and stunning, pristine speleothems—or cave formations. Postojna and nearby Planinska jama are home to the proteus anguinus, an endangered aquatic cave salamander affectionately called the “human fish.” During Christmas, a nativity scene is erected in Postojna and more than 500 people gather in a single chamber to witness a festive performance staged among the stalactites and stalagmites.

“Slovenia is commonly thought of as the birthplace of recorded cave exploration,” says Kosic Ficco. “It provides variety of caves and enables everyone to go underground. From easy tourist caves to the deepest pit in the world (Vrtoglavica), everyone can find something suitable for their skills.”

POSTOJNSKA JAMA: The Pivka river runs through three contiguous cave systems that together comprise Postojnska jama. They include the famous Postojna jama, the Pivka jama and the Crna jama (Black Cave). Here, Shone says he was surprised to discover some of the darkest limestone he’d ever seen. Shone adjusts his light power depending on the colour of the rock, and whether it is very reflective or very light absorbent. He needed quite a bit of power to capture this chamber. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

LIGHTING UP AN UNDERGROUND WORLD

For Shone, photographing what is considered a “mecca” destination among cavers was the realization of a longtime dream.

As a child, Shone learned how to draw and paint watercolours from his father. As a teenager, Shone spent weekends at the Lake District, a national park in the U.K., tramping through the hills and painting landscapes in the same vein as Constable and Turner. Shone landed at the University of Sheffield to obtain a fine arts degree while simultaneously pursuing his newfound love of rock climbing on the local Gritstone.

When Shone was 19, a climbing friend and fellow student persuaded him to go on a weekend caving trip in northern England.

ZELSKE JAMA: At one point, no skylight existed here in Zelske jama; it was all just an underground chamber. Over time, though, the weight of the overhead rock became too great for the steadily dissolving structure that once supported it. It collapsed, forming a sinkhole. For cavers, the hope is to not be “lucky” enough to ever witness the formation of one of these features from below. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

“I did not like the idea of going into a cave, into a black, dark space underground where there’s water, dirt, no sunlight,” says Shone. “As a climber, caving sounded so claustrophobic.”

Shone, despite his best instincts, went anyway and soon found himself at the edge of a rim, contemplating an abseil into a dreadful, black abyss.

The Reka Reka is responsible for the dissolution and erosion of Križna jama chambers, while the slow process of dripping water deposits minerals on the floor and ceiling that create the cave’s otherworldly speleothems, such as this stunning white formation on the right. Formations can begin as either stalactites or stalagmites, but when they finally connect ceiling to ground, they’re called columns. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

PLANINSKA JAMA: The team, left to right: Joe Myer, Uroš Kunaver, Katarina Kosic Ficco, and Mike Ficco. Shone and Mike Ficco are longtime caving buddies, and Katarina Kosic Ficco, who met Shone through Ficco, her husband, is a native Slovenian born and raised in the Karst region. Kosic Ficco is a PhD candidate in karstology at University of Nova Gorica, through Karst Research Institute, Slovenia. She was integral to securing the access this team needed to see parts of the caves not open to the public. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

“The adrenaline was so intense. One moment I was standing in this nice sunny, grassy landscape, and within about five seconds, I was plummeting into this completely alien world that I’d never experienced before,” recalls Shone. “It was pitch black, there was a lot of shouting, and roar of the waterfall was so loud I couldn’t even hear myself.”

“But at the same time, I was just absolutely transfixed. It was unbelievable. I’d never felt anything like it before, and I was instantly hooked.”

Shone returned to Sheffield after that first weekend and felt an artistic compulsion to try to recreate the experience the only way he knew how: on a canvas. However, he quickly realized that painting would be an inadequate medium. He went down to the university’s darkroom and borrowed a camera, a moment that ended up changing the course of his life.

PLANINSKA JAMA: With lower river levels, it was quite common for the team to have to portage their raft across the shallower and drier sections of the riverbed. Here in the Planinska jama, the team makes their way toward the meeting of the Rak and Pivka rivers, one of Europe’s largest underground confluences. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

For Shone, these twin passions for photography and caving emerged virtually concurrently, then grew in parallel over the next 18 years.

Photographing a dangerous pitch-black room appealed to Shone’s adventurous side, while the technical challenge of working with lights stoked him as an artist.

“Because I’ve got this background as a painter, I’m trying to ‘paint’ with my lights,” Shone says. “It’s not just a case of lighting up some walls and saying, ‘OK, that’s done.’ I’m trying to paint a picture by moving the flashes around, making creative choices about what to highlight and what to leave dark. I’m trying to make it feel like it’s been lit up naturally, which of course is the ultimate challenge because it’s pitch black down there. It’s what I’ve been doing for the last 18 years, and, well, I’m still trying to get it perfect.”

ZELSKE JAMA: To capture the incredible size of this watery chamber in Zelske jama, Shone had three teammates don wetsuits and tread water while each holding Shone’s powerful single-use flashbulbs. It ended up being technically challenging to get all three bulbs to fire at the same time, and each time they had to reload, they needed to swim back to the edge in order to stand up and put in a new bulb. This type of technical challenge, however, is all in a day’s work for a cave photographer. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

 

Lead image: KRIŽNA JAMA At 27, 43m, Križna jama, aka the “Cross Cave,” is nearly as long as Mount Everest is tall—yet it’s still considered a moderately sized cave for Slovenia. Križna jama is a beautiful and heavily protected cave system (fewer than 1,000 permitted entries per year) filled with interconnected emerald green pools that are mainly fed by the Bloke plateau. Križna hosts a rich biodiversity that makes it one of the largest single ecosystems in the world. - PHOTOGRAPH BY ROBBIE SHONE, NATIONAL GEOGRAPHIC

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