The legendary Idrija mercury mines – UNESCO World Heritage in Slovenia

Tunnel in the Idrija mecury mines, Slovenia

Whenever we travel, we usually have a look at the UNESCO World Heritage sites in the country. So, when we spent a week in Ljubljana we tracked down as many of the buildings as possible by the architect Jože Plečnik. The Idrija mercury mines were another UNESCO site, we figured, that we could visit in a day trip from the capital.

So, we made our way by public bus from Ljubljana to the small town of Idrija on a grey and rainy day. Just the right setting for a visit to the mercury mines of Idrija.

What is special about the Idrija mercury mines?

Along with the mines of Almadén in Spain, the Idrija mercury mines have the prestigious status of a UNESCO World Heritage since 2012. In the historic mines of Idrija, mercury has been mined as early as 1500. The mines were active until the 20th century and belonged to the biggest mercury mines in the world for centuries.

Anthony's Tunnel in Slovenia, opened in 1500

Apart from the historical importance of the mining itself, the mining conditions also shaped everyday life. Around the mines, a prosperous mining town evolved, complete with miners’ living quarters, a theatre, and later some manufacturing industry.

Who needed all this mercury?

A shiny, liquid metall forming silvery droplets? Mercury is absolutely intriguing! In the 10th century the Caliph of Cordoba had a small mercury pool to impress his visitors with light effects. During the 16th century Spain needed mercury to extract gold and silver from ore in their new mines in South America. Mercury easily combines with precious metals turning it into an amalgam. This amalgam could be quite easily separated into pure gold and mercury again. The mercury from Idrija was exported to Germany and Holland and from there it went to South America. Especially the German Fugger family made a fortune from the mercury trade. Later the Idrija mercury was also used for scientific instruments and in the production of modern weapons.

A visit to the Anthony’s Tunnel in Idrija

From the bus station it is only 400 m on foot to the entrance of the Antonijev Rov or Anthony’s Tunnel. This simple building is one of the oldest preserved mine entrances in Europe and a visit into the Anthony’s Tunnel is only possible with a guided tour. So, we are lucky that one of the tours starts just when we arrive.

Anthony's shaft identity badges

The tour begins with an introductory movie in the former assembly hall. This large hall was not for festivities but the place where the miners gathered before their shift to get their job assignments. When they went down into the mines, they wore an identification tag. That was a small, numbered medallion, which they put back on a board after work. The intention was to check if everybody had returned safely from underground. Imagine those days when miners were missing in the evening! It must have been scary and depressing. And in fact, in the 500 years the mine was active, around 300 miners died. Still, this is quite a low number in comparison to other historic mines, we learn.

 “Srečno” is written over the entrance to the mines – Slovenian for “Save return”. Today we wear safety helmets and a protective raincoat and follow our guide Matic into the narrow rock passages.

Hard hats for the Idrija mercury mines

Mercury – a poisonous metal

Work in the mines was not only dangerous but also quite unhealthy. Although it is considered a metal, mercury is liquid at room temperature! In the Idrija mercury mine, around 30% of the mercury occur not as a compound (which is usually solid), but as pure mercury contained in the rocks. And indeed, even today, walking along the rocky walls, we see glittering silver droplets in fissures of the grey stone. These are tiny balls of pure liquid mercury, held together by surface tension. For the safety of the visitors there is a plexiglass screen in place in front of most of these droplets.

We remember the old-fashioned fever thermometers from our childhood, which always came with a warning. “Stay away from them,” the adults would caution us, because if the glass breaks and the mercury leaks out, it is highly poisonous. Inhaling a certain amount of mercury fumes can have a negative effect on the body and lead to cancer. 

„As children we played with the shiny liquid pearls,” our guide Matic recounts. “We had no idea that these droplets are toxic.”

Today it is well established that a quite high number of miners got a mercury poisoning. And even today the cancer rate in Idrija is higher than in the rest of Slovenia. The official advice is now that the inhabitants of Idrija should not grow vegetables in their gardens because of the heavily polluted soil.

In the Idrija mercury mines, safety measures have been lenient at best throughout history. Safety clothing such as masks and gloves were only introduced in 1960s.

History of the Idrija mercury mines

It was in 1490 that a barrel maker found mercury in the water, thus starting the mining operation in the small town. As demand grew, the mines became ever bigger. And with the invention of the steam engine in the 19th century, the output of the mine increased further. Eventually the Idrija mercury mines were among the most technically developed mines in Europe.

In the early 20th century, however, the presence of a lot of water in the rock became a problem for the electrification of the mines. Nevertheless, the mines reached their peak output in 1913, at 820 tons of mercury. After World War I, the mines belonged to Italy for some time before becoming part of Yugoslavia. But they suffered from economic crises and became ever less profitable. They finally closed for good in 1988.

Daily life in the Idrija mercury mines

In the Anthonys Tunnel of the Idrija mecury mines, Slovenia

The tour through the Idrija mercury mine takes around one hour and leads us deep into the rocks. Inside the mine, life-sized puppets mimic the life of the miners and give an impression of the work in the mines. Compared to other mines we have seen (like Blaenavon in England or the mines at Banska Stiavnica in Slovakia) the mine waggons seem small. That’s because mercury is exceedingly heavy: 14 times as heavy as water! Accordingly, the small waggon the size of a removal box could hold up to 300 kg of ore and mercury!

Mine waggon in the Anthonys shaft, Idrija mecury mines, Slovenia

The regular miners worked only two 8-hour shifts. The third shift at night was reserved for the dynamiters. At the end of the tour, we see a virtually recreated blasting of a tunnel section. At that point we are about 80 m deep under the mountain, and we don’t want to imagine how a real explosion would feel. It does make sense that we pass a chapel inside the mine at the end of our tour.

The miners' chapel inside the Idrija Mercury Mines

Visiting the mercury smelter and the museum

The mercury mining business did not stop in the mine itself. In fact, the whole town was created around the mercury processing facilities. There was an ingenious, continuous ore movement system that moved recently mined ore up and out of the mine. From there it moved in a kind of ropeway across the river valley to the smelter on the other side of the small town.

So, after the mine, we also visit the remains of the smelter. In the smelter, the mined ore was first crushed and sorted and then transported to the smelting furnace by conveyer belts. The remains of the furnace are still quite impressive: Basically, it is a 36 m long, 2 m diameter, slightly inclined pipe. This pipe was heated throughout, while the crushed ore was gliding down inside. Mercury turns into gas at a temperature of 356 °C. At some point inside the pipe, the mercury would turn to gas and float up so that you could separate it. The gaseous mercury was then cooled down again and collected. The work in the smelter with its gaseous mercury was even more hazardous for health than the work in the mines.

Rotary furnace in the smelting plant of Idrija

In the adjacent museum we learn more about the different uses of mercury. For instance, the Swiss alchemist and physician Paracelsus in the 16th century advocated mercury to treat Syphilis. He died of mercury poisoning himself, however. In 2011 mercury was banned in the EU.  And in 2017 the so-called Minamata Convention, designed to protect human health and the environment from emissions and releases of mercury, became effective.

Where else in Idrija can you see remains of the mining history?

The mining history of Idrija is present everywhere. But if you want to see more remains of the actual mining there is the area of the Joseph’s shaft (Jožefov Jašek) a bit up the mountain. You cannot enter this shaft, but there is an old waterwheel to see and some administrative buildings from the mining area. We went there at dusk when it was still lightly raining.

Mining entrance to the Joseph's shaft

Should you visit the Idrija mercury mines?

We think that the Idrija mercury mines are fascinating evidence of a now-forgotten industrial history. In many countries, there are old mines. And often, they have insightful museums – in the German Ruhr area, for instance, you can explore the whole industrial heritage through numerous museums and old coal mines.

It was also quite interesting to learn more about mercury. Mercury was still present in daily life in our childhood but is very distant now. It is usually only in books and archaeological records that we find references to mercury. For instance, we often visit sites and museums relating to the silk road in Central Asia during our guidebook research. We have been to ancient cities like Paikent or Akyrtas, but also the historical museums in Samarkand or Tashkent. These museums often display “mercury flasks” of clay. Apparently, the scientists producing the famous glazed tiles of Uzbekistan and Persia also used mercury. For gold making, or to extract their ingredients for the shiny glazes. 

Mercury bottles from Central Asia, 10-12 century AD

How to get to the Idrija mercury mine from Ljubljana

We took a bus from Ljubljana bus station (next to the train station). They did not go very often – less than every hour – so we had checked the timetable for both directions beforehand. The bus cost 6,30 € each way (in 2022) and took just over an hour.

NB: We were not sponsored or paid in any way to write this blogpost about the mercury mines of Idrija. We paid all expenses ourselves.

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  1. Thanks for sharing your very unique experience! I love your off the beaten track trips/explorations. Not sure from where/whom I got it from but I remember as a kid I had a vial of mercury that I’d would play with for hours. I knew it was poison but was still fascinated by it. It was the early 70s so we played with anything we can get our hands on.

    1. I can imagine that it was a fascinating toy – I guess anything that keeps a decent amount of surface tension is fascinating. And mercury is shiny on top of that!

  2. We too track down the UNESCO sites when we travel. But I must admit I might not have thought of visiting a mercury mine. I did not know that mercury was a key element in mining gold and silver! Good to learn more about the mining process at the Idrija mercury mines. And to understand why the sign reads “Safe Return” over the entrance to the caves. Although the mining is not only the dangerous part of dealing with mercury! Interesting to visit the other areas around town that supported the mining of mercury.

    1. Dear Linda, we did not know what to exprect from the visit of the Mercury mines in Idrija as it was not possible to get reliable information. But it turned out to be a fascinating day trip from the capital of Ljublijana.

  3. The Idrija mercury mines are an impressive landmark and I understand why it’s a UNESCO site. I definitely didn’t come across this when we were in Slovenia but will bookmark it for next time. The museum and the smelter looks interesting, but I can’t stay in the mines as I’m quite claustrophobic.

    1. Dear Lisa, I can see that it is difficult to visit a mine when you are claustrophic. I would say the Anthony tunnel was the highight of the visit. The museum was interesting too but somewhat overdetailed.

  4. Your blog post gives a really cool insight into a unique piece of industrial history that many of us might not know much about. I love reading your description of the tour inside the mine and the shiny liquid mercury droplets. It’s also pretty eye-opening to learn about the health hazards associated with mercury exposure and its long-lasting impact on the environment.

  5. I didn’t know that today’s Slovenia has played such an important role in the production of mercury. I do remember indeed that mercury was a “danger” in my childhood, with my parents always telling me not to play with the thermometer because if it breaks it’s very toxic. it’s such a shame to read that people in Idrija are still getting sick and that the cancer rate is among the highest in the country. I can imagine seeing the mercury droplets in the mine, on the rock walls, was fascinating.

  6. This place is interesting and thank you for sharing your unique experience. It is nice that they declared this as a UNESCO site to remind us of the forgotten industry history. I am not sure if I am up for a visit since I am pretty scared of mines and closed spaces.

    1. Dear Clarice, thanks for your thoughtful comment. Yes, I guess if you scared of closed places you should avoid a visit to the Idrija mercury mine.

  7. Such an unique place to visit in Slovenia! I was not aware that mercury was needed to mine for gold and silver. I know mercury is dangerous and that a thermometer can break easily releasing this dangerous element. But it is shocking that many people in Slovenia are still getting sick and dying of cancer due to mercury exposure. I loved reading and learning so much about the mercury mines in Slovenia. 🙂

  8. It was true that we liked to play with mercury when we were little and didn’t realize the danger of it. I’m not sure whether I want to go 80 meters deep into the mountain, though. I have a claustrophobia, and seeing your first picture was enough to make me dizzy. Hehe.. It’s interesting to see how they used mercury for different things, like a cure for syphilis.

  9. Oh wow! I learned so much about the Idrija mercury mines but also mercury. I didn’t realize mercury could be mined — I’ve only ever seen it as a liquid in science class or thermometers. It’s also a shame that so many mine workers (coal here in the US) get sicknesses from what they are mining. And going back to the 1500’s! They were so much more ingenious back then. Thanks for opening my eyes to something new and different!

  10. I’d love to visit the idrija mines, I have become really interested in industrial history on my travels ( we only have slate in our area). I didn’t realise that mercury was used for extracting gold or that it could be so easily separated once it had been used. It’s interesting reading about the use in weaponry and understanding the risks that went along with mercury mining for the workers.

  11. What an interesting place to visit and to learn about how mining worked. Scary to think about wearing a tag in case workers encountered the dangers of mining. This sounds like a fascinating tour.

  12. I’ve been only to Ljubljana, but ever since, Slovenia has been high on my list. In addition to the beautiful lakes I’d like to visit, you’ve put another inspiring place on my itinerary. As a matter of fact, your Korea-Posts were a nice inspiration for my recent trip. I was remembering your post while I visited the Haeinsa Tempel in the pouring rain 😀 Hence, next time I’ll remember you while exploring a mercury mine 😉

    1. Dear Renata, really happy to hear that you found our Korea posts useful! I think you would enjoy a visit to the Mercury mines. We liked Slovenia a lot too – the lakes are also on the list for another trip. And there are some nice climbing areas along the coast. Hargh – so many places to go! Happy travels!

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