Half a century after the first humans landed on the Moon, the spirit of space exploration remains alive in the depths of Earth.

Last September, six astronauts entered a maze of underground rivers and passages in the Slovenian Karst Plateau to prepare for exploration of other worlds. Their steps followed those of the pioneering cavers who in the 17th century tried to map the path of water flowing under the surface, and described for the first time a small living creature in the cave.

The CAVES 2019 edition took place “where everything kind of started,” says Borut Lozej, ranger at the Škocjan caves park. These caves have a long history of exploration, and this year is the 200th anniversary of their opening to the public.

Up and down the cave walls. Credits: ESA–A. Romeo

“This Karst area is one of Europe’s natural wonders and where speleology was actually born,” says Franci Gabrovšek, professor at the Karst Research Institute ZRC SAZU in Slovenia.

ESA’s latest training adventure equipped an international crew with the technology and skills to explore uncharted terrains on the Moon and Mars, this time with a focus on searching for water.

A long, mostly uncharted underground river makes this area special. The river is believed to be over 60 km long. “We have barely explored ten percent of it. This is the greatest example in the world of a subterranean river, and still largely a mystery,” explains Tullio Bernabei, CAVES logistics and rigging expert.

Discovering cave paths. Credits: ESA–A. Romeo

“Yet after all this time, every year we discover new paths. We are proud to see astronauts from different space agencies coming here to continue exploring,” adds Borut.

The pioneers

The story behind the exploration of these caves tells us about the search for water and the courage of the early cavers. Known as the ‘grottern arbeiter’ in German, these workers became the first true speleologists.

“They were very brave people who did impressive things, risking their lives to explore, and sometimes losing their life in the process,” says Tullio, director of the film Grottenarbeiter: Il fiume della notte.


The film follows on the steps of the explorers searching for the river. The ‘cavenauts’ watched the film as an introduction to the quest for water during cave exploration.

“Considering the caving techniques of those times, it is truly incredible what those explorers achieved in the 1890s. They climbed through any possible opening that they could see, even if this was 100 m above a canyon,” recollects Franci.

Nowadays, over 12 km of pathways carved over 100 m-high walls are testimony of their amazing work. “Driven by the curiosity of genuine explorers and the perseverance of hard workers, they were well ahead of their time,” points out Franci.


To not forget the investment and trails of the early explorers renovation work started in 2003. The first signature in the visitors book was signed 200 years ago and two centuries later to the date, the park is reopening a 1500 m-long trail for the public, known as the Via Ferrata.

The CAVES 2019 astronauts followed that path resembling spacewalk procedures, equipped with tethers and listening to a podcast of the book Into the Unknow: The story of Skocjan caves.  

‘Cavewalking’. Credits: ESA–A. Romeo

“At the end of the 19th century you could reach the bottom of the shaft by foot on the Via Ferrata trail,” explains Borut. The park wants to continue the repairs an intensive cleaning of the cave to completely rebuild the original infrastructure. 

“As the early explorers of these caves used to say, we are only beginning to understand what is hidden under our feet, beneath the surface. Big discoveries are yet to come,” states Borut.

This image was taken to reenact the path of exploration followed by early cave explorers. Credits: B. Lozej