Some general information
What is karst? Karsts are limestone plateaus, characteristic of the Dinaric Alps and transnationally - Slovenia, Croatia, Italy - from which emerge reliefs formed by the dual hydraulic and hydrochemical erosion of the rock. This erosion has formed cavities, dolines and faults, particularly below the earth's surface, which has allowed the development of a vast network of underground waters and caves. These caves are home to a unique ecosystem of flora and fauna that never see the light of day. A large part of this breathtaking landscape was designated a biosphere reserve by Unesco in 2004.
In Slovenia, some twenty caves are open to the general public, and another fifty or so to more experienced visitors. Of course, you'll need to be suitably equipped, as humidity levels are very high and the average temperature rarely exceeds 12°C.
Slovenia has a wide range of caves, since 50% of the country's soil is limestone. They are mainly found around the Kras region, west of Ljubljana, towards neighbouring Istria.
The complexity of the study of karst
The main research center, at the forefront of karstology worldwide, is located in Postojna. Launched in 1947, it is home to renowned scientists whose aim is to study karst phenomena that are still largely unknown. They publish in the internationally renowned journal Acta Carsologica. Their research focuses on a wide range of topics, from the formation of groundwater to the establishment of animal life underground. In particular, they have established that half of Slovenia's population is supplied by karst water. Slovenian caves, most recently the Divaška cave, also serve as a training base for Nasa astronauts, who test delicate living conditions in darkness, silence and permanent humidity. Last but not least, a Karst Museum was inaugurated in Postojna in 1992, making a major contribution to the collective effort to popularize science.
Caving, a national sport
There are over fifty caving clubs and associations across the country, grouped together under the umbrella of a federation. Their activities range from exploration and observation to guided tour expeditions, educational activities for schools, safety supervision in caves open to the general public, and assisting and rescuing people in peril. They also issue a permit, which is mandatory for advanced caving and exploration of certain caves requiring this document.
A little-known discipline: biospeology
This is the study of the way of life of cave-dwelling organisms. Researchers are trying to answer such fundamental questions as: How did they get here? How have they adapted to this unique underground environment? What do they eat on a daily basis? Broadly speaking, there are three categories of cave-dwelling animals. The first are the troglobies, which have totally adapted to life underground, such as certain crustaceans, fish or amphibians like the protoea anguillata. The second category is known as troglophiles, who mainly use the underground world as a living space. These include birds such as the cave guacharo, and insects such as spiders. Finally, trogloxenes make partial use of the cave for comfort - hibernation for bears and bats, for example - or as a temporary refuge for rodents.
Large-scale underground tourism: the examples of Škocjan and Postojna
Located in the municipality of Divača, close to the Italian border, the Škocjan Caves form the world's largest underground wetland. The impressive flow of the Reka River breaks the silence for a few minutes. The ecosystem here is particularly well preserved, and it's not unusual to come across a few species of bat! The discovery of the dead lake (Mrtvo Jezero) prompts meditation. We are reminded of Sigmund Freud's words on his visit in 1898: "If Dante could have seen something like this, he wouldn't have needed to stretch his imagination much to describe the Underworld." The site was declared a UNESCO World Heritage Site in 1986, and 100,000 visitors flock there every year.
The Postojna cave is impressive for its sheer size, with 24 km of underground galleries. This almost baroque ensemble attracts an exceptional fauna: the famous protée anguillard, the beetle, disconcerting-looking crustaceans and numerous spiders. However, the other side of the coin is obviously the massification of tourism in Europe's most visited cave - 40 million visitors since its discovery and over 500,000 a year: the ecosystem has been disrupted and tends to shun contact with tourists. Although not listed by Unesco, the cave has established its own model for underground tourism, designing a small train that allows visitors to thread their way through these obscure cavities - it's been around since 1872! -but also a lighting system that lends a certain glow to these grandiose landscapes.
Cave tourism is an ancient practice, inspired by discoverers and writers such as Édouard-Alfred Martel - founder of contemporary speleology and visitor to Postojna - and Jules Verne. Speleologists encouraged early protection of these fragile sites, which has ensured that they remain in good condition to this day. The massification of tourism, particularly at Postojna, now poses new challenges in this area.
Other caves to discover
It's difficult to be exhaustive in this area, as Slovenia is packed with caves, each more impressive than the last. The Križna cave, south of Postojna, offers a prodigious display of stalactites and stalagmites, as well as views of several underground lakes. Only the dry parts can be visited on foot; the rest of the exploration is by boat. A few kilometers away is the Planina cave, home to one of Europe's largest confluences of underground rivers. The aquatic spectacle is truly breathtaking.
Further west, in the direction of Trieste, is the Divaška cave, discovered in 1884. Its indelible limestone deposits are well worth a visit. Local legend has it that Sigmund Freud visited it. The nearby Vilenica cave is known as the oldest visitable cave in Europe, dating back to the 17th century. Finally, further away, in the center of the country on the Velenje-Celje axis, lies the Grotte de l'Enfer, where you can marvel at Slovenia's highest underground waterfall.
