Deep within the Slanské Hills in Eastern Slovakia lies one of the world’s most mysterious treasures: The Historic Opal Mines. A subterranean labyrinth where rare opals are born. Slovak opals are globally renowned for their intense play of colors, a phenomenon known as opalescence. For centuries, these stones were ranked among the most precious gemstones on Earth.
Located southeast of the city of Prešov, between the villages of Zlatá Baňa and Červenica, you will find the world’s oldest opal mines, also known as the Dubník Mines. Beneath the surface lies a fascinating maze of approximately 30 kilometers (18.6 miles) of mining tunnels spread across 17 levels—five of which are currently submerged in crystal-clear water.
After operations ceased in 1922, the mines fell silent for nearly a century. It wasn’t until 2015 that they were reopened to the public, thanks to the passion of volunteers dedicated to giving this piece of world history a new lease on life.
An Underground Trek for the Treasures of the Slanské Hills
Today, visitors can explore a portion of this hidden world on a guided tour. The route is approximately 1,280 meters long and winds through ancient tunnels where generations of miners once toiled.
The atmosphere underground is one of profound silence and chill.
- Temperature: Stays between 0.5°C and 6.4°C (33°F – 43°F) year-round, so a warm jacket is essential even in mid-summer.
- Duration: The tour lasts 45 to 60 minutes, covering history, geology, and mineralogy.
Some visitors claim to feel a strange energy in these tunnels. Perhaps it’s just the play of shadows, or perhaps it’s the lingering stories of the miners who searched for “fire in the stone.”
The Gemstone That Enchanted Emperors
Slovak opals gained global fame in the late 16th century, but their “golden age” came when the Viennese jeweler Salomon Johann Nepomuk Goldschmidt leased the mines.
His son, Adolf Goldschmidt, showcased the Dubník opals at the 1873 World Exhibition in Vienna. The success was so immense that he was granted a noble title and the predicate “Libanka”—named after one of the local mining sites.
Even the family of Emperor Napoleon was captivated by these gems. Empress Josephine famously wore a magnificent Slovak opal known as the “Trojan Fire.” The largest opal ever found in this region is called the “Harlequin.” It weighs a staggering 594 grams (21 oz) and is currently housed in the Museum of Natural History in Vienna.
A Geological Rarity: Fire in Ancient Volcanoes
The Slanské Hills are the remnants of ancient volcanoes. This 50-kilometer-long mountain range is composed mainly of andesite and tuff. It was within these volcanic rocks that opal veins formed millions of years ago.
The highest peak, Šimonka (1,092 m / 3,583 ft), overlooks a wild landscape of dense forests and old lava flows. For a long time, these mines were the only known source of precious opal in the world until new deposits were discovered in Mexico and Australia in the 19th century.
To this day, the Slovak Opal remains unique—it is the only precious opal found naturally in Europe and Asia. In 2016, it was officially granted a Protected Geographical Indication.
A Sanctuary for History and Nature
The abandoned sections of the mines aren’t just for tourists; they are a vital ecological site. Since 1964, the area has been protected as a sanctuary for several species of bats.
It serves as a crucial wintering ground and was the site of the first discovery of a hibernating colony of the Parti-colored bat in the former Czechoslovakia. Today, the location is part of the European Natura 2000 network of protected habitats.
A Treasure with Secrets Yet to Be Revealed
The opal mines in the Slanské Hills offer a unique blend of history, nature, and adventure. With only a small fraction of the 30-kilometer network open to the public, much of the mine remains shrouded in darkness. Who knows what else lies in the depths? Perhaps more opal, or perhaps just the eternal silence of the earth. Either way, it is a piece of history that everyone should see at least once.
