Baby dragons, crazy dripstones and magnificent halls – what more could you possibly want in a cave?

When it comes to Postojna cave, it’s hard not to talk in superlatives. Often called the queen of the underground, the large Karst cave system in southwestern Slovenia has had a very early tourism start because of its easily accessible beauty and soon became the first cave in the world with an underground railway. As it is home to the the very strange endemic human fish, it is also known as the cradle of speleobiology, the biology of cave creatures, but let’s start at the beginning.

Postojna cave gets its name from the nearby city of Postojna and is part of one of the longest cave systems in Slovenia and also one of our main tourist attractions. It was first opened to the public in 1819 and soon became world famous after the visit of the Austro-hungarian emperor, who was very impressed by the wondrous underground world he saw. Back then they used giant chandeliers and torches to light up the cave for visitors, who came from allover the world. In fact, the cave became so popular, that the first cave railway in the world was installed in it in 1872, as well as electric lights in 1884, which was earlier than in the Slovenian capital, Ljubljana, or in certain parts of London. You can still see the soot from the candles and torches in the main part of the cave and the tourist railway remains a major part of Postojna cave’s attraction to this day.

Today the railway cars are no longer pushed by tourist guides, but rather by electric locomotives and you can visit 5.3 kilometres of the cave as part of the regular tour. As you can imagine, Postojna cave is extremely popular and often overcrowded, so we Slovenians tend to forget how amazing it is. However, we really shouldn’t and although Slovenia has many other gorgeous, less popular Karst caves, I would recommend a visit to Postojna cave to anyone, no matter how touristy it is, because it is so popular for a reason.

Due to its shape and size, Postojna cave was uniquely suited to the construction of an underground railway and the cave train ride is the first experience when visiting, no matter which tour package you select. The ride is about 4 kilometres and is a special experience in itself, as the train takes you to the main part of the cave through winding tunnels and large halls, all of them strategically lit to highlight the beautiful rock formations Postojna cave is famous for.

Since the whole cave system is so large and diverse, you pass through narrow tunnels, frighteningly close to limestone overhangs, and magnificent halls with bizarrely tall ceilings lit by fancy glass chandeliers, which will almost feel like they shouldn’t exist underground at all. There’s even a Concert hall inside Postojna cave, which can hold up to 10.000 people and is often used for events, which you will see at the end of the cave tour, along with a souvenir shop (of course) before you board the train back to the surface again.

Entering Postojna cave

The trains are quite fast, so I felt a bit frozen by the end of the ride. The temperature inside the cave stays at around 10°C during the whole year and the ground is always wet, so you should definitely dress warmly and wear proper shoes. Don’t go prancing in wearing sandals, because exploring the main parts of the cave is done on foot for about an hour and a half. The path is extremely easy, paved and accessible to everyone, although it can be a bit slippery.

Obviously the cave can only be visited on a guided tour and they are available in different languages, along with audio guides for additional languages. The first stop after the train ride is the main and the oldest known part of the cave, consisting of high halls full of crazy rock formations called dripstones or flowstones. This area is usually crowded with all the many tourist groups, which can make it hard to admire the cave at your own pace, but it does get better later on when the trail is narrower.

The main part of the cave and the Russian bridge

At the end of the main part is the Russian bridge, a rather Khazad-dum-ish bridge spanning the chasm between the main part of Postojna cave and the so called Beautiful caves. It was built by the Russian prisoners during World War 1 and allows easy access to the prettiest part of Postojna cave.

However, before we get to that, here’s a bit of theory first: as a Karst cave, Postojna cave owes its beauty and existence to the erosion of soluble limestone, which dissolves in water and is a geological phenomenon in my part of the world. I’ve already written a bit about Karst here, and there are two great spots where you can learn about the formation of the cave and its history: the Expo Cave Karst interactive exhibition centre next to the cave entrance and the Notranjska museum in Postojna, which also houses the shiny treasures from the nearby Predjama castle, another spectacular attraction in the vicinity of Postojna cave.

The dripstones inside Postojna can be divided into two groups depending on their formation: stalagmites are the dripstones growing from the floor up, while stalagtites are the dripstones hanging from the ceiling. Both are formed through deposition of limestone, when the water full of dissolved limestone drips down from the ceiling to the ground. It can either drip to the floor where the limstone builds up, or it can flow along an existing dripstone hanging from the ceiling and deposit the limestone at its tip.

The process takes thousands of years as the average rate of dripstone growth is about 1 milimetre per 10 years. The oldest stalagmite you can see in Postojna is 16 metres high, which makes it about 150.000 years old. You can see a cross section of a dripstone below and I can also tell you that if I were a dripstone, I would be about 16.500 years old.

About Karst caves

Hopefully this gives you a better idea of the magnificence of Postojna cave, as its size and the complexity of its shapes and passages truly defy belief. It’s hard to convey the awe-inspiring, terrifying feeling of age and permanence inside the cave in writing, because it’s impossible to really comprehend the number of years it took for the cave to form – patiently, one drop at a time. The good news is, that it never feels claustrophobic, as it is easy to forget about the crushing weight of the tons of rocks above you in the high halls.

You really ought to experience it for yourself, and this brings us to the most beautiful part of Postojna cave: the Beautiful caves. This part was discovered a bit later and consists of 3 halls with what are rightfully called the most amazing formations in the cave. The first is Spaghetti chamber, which is full of tiny, thin stalagtites hanging from the ceiling that really look like spaghetti, followed by the White and the Red chamber. Both are known for their distinct limestone colours: the white represents the purest limestone, while red is the result of iron deposits.

Beautiful caves

The basic tour of Postojna cave takes you through the Beautiful caves to the Concert hall, where you’ll pass the two signature dripstone pillars on the cover photo of this post. The fancy white one is called Brilliant and is hailed as the most beautiful dripstone in Postojna cave, along with the ornamented pillar next to it.

The Concert hall is where the tour usually ends, but the last time I visited in 2020, my boyfriend and I took advantage of a promotional offer and choose the option of trekking through 3 caves instead of just one. Our tour group was smaller than the regular tours and we visited Postojna cave, the Black cave and Pivka cave. The whole thing lasted about 3 hours and was a relatively easy trek on a well-maintained path through the caves. You can see a map of the whole cave system formed by the river Pivka below – we actually went through most of it, as parts of the caves are underwater or only accessible to trained spelunkers.

The tour took us through a manmade tunnel between Postojna cave and the Black cave, which was built as part of a military endevaor to connect the Postojna cave with a cave close to the Italian border, which apparently never happened. As it turns out, the Black cave is actually a part of Postojna cave, but was discovered separately and it took them a while to realise the two caves were connected.

The Black cave is, as the name says, black. All of it is covered in ancient soot, which was most likely the result of an extensive forest fire years ago. The soot was probably blown into the cave by the wind and it will take thousands of years more for the dripstones to clean themselves. In the meantime, it’s beautiful, somewhat dystopian and very cold. The temperature inside the Black cave stays at about 6°C the whole year round and let me tell you, it’s a temperature shock when you have to climb out to the surface during the summer.

What struck me the most about the Black cave though, is how fragile the cave ecosystems really are. The idea that something as simple as a forest fire, no matter how massive, can affect a cave for so many years in such a way, got me thinking about human pollution and industrial waste, which is an everpressing problem for rivers. Since Karst is a sensitive type of terrain and caves strongly depend on their underground rivers, the Black cave is a visible reminder of the potential consequences our continued dismissive attitude towards the environment could have on the underworld – as above, so below.

Black cave

But, back to the trekking tour: after a short walk up on the surface following the road to Pivka camp, we entered our final cave of the day, Pivka cave. Now, Pivka cave may not be quite as beautiful as Postojna cave, but it is wilder and there’s a river in it. The Pivka river runs right through Pivka cave, which gives it a special vibe and the reflections in the water are absolutely gorgeous. Although it is a bit rougher around the edges, or perhaps because of it, Pivka cave is also well worth a visit.

In fact, if you can afford it, I would heartily recommend the trekking tour through the 3 caves, as it is really more of a walk than a trek and you’ll get a more authentic cave experience. Although Postojna cave is so beautiful, it is also so very touristy and civilised, that walking through it feels more like walking through a museum than a cave at times. While it’s certainly worth visiting because of its unique beauty, I would also recommend a visit to the Škocjanske caves, another Slovenian Karst cave system on the UNESCO Heritage list, which is a lot less popular and feels more like a cave should.

Pivka cave

After our visit to the Pivka cave, we retraced our steps through the Black cave back to the Postojna cave, where we got to meet the best kept secret of Postojna cave – the baby dragons. The human fish or olms are a fascinating species of cave critters that have boggled the minds of locals and scientists alike for years. Back in the days of yore, when the Pivka river flooded through the undergrond sinkholes, it would wash out bizarre tiny white creatures that the locals assumed were baby dragon larvae or something. Legends claimed that a dragon lived in Postojna cave and these were its spawn.

The olms look like pale, translucent snakes with no eyes, tiny feet and red tufts and are endemic to the Dinaric Karst caves, so Postojna cave is one of the few spots around the world where they can be found. Due to their skin they were nicknamed the human fish and were so weird, that scientists from allover the world came to study them. Even Charles Darwin wrote about them in his On the Origin of Species and Postojna cave is known as one of the cradles of speleobiology, because lots of cave organisms were discovered there due to the olms’ fame.

As it turns out, the olms are not only very strange, but also superanimals. They are extremely sensitive to light and have incredibly sensitive skin receptors, which allow them to sense the world around them and even electromagnetic fields. They are the ultimate cave predators, live for up to 100 years, can regrow their limbs and survive without food for up to 12 years (apparently some scientists forgot about them during the war and found them alive in a closed lab), but they are pretty bad at procreation. Since they only live in specific conditions, they are inherently endangered and biologists had been trying to figure out how they breed for years (they only breed every 6 or 7 years).

Well, eventually one of the olms conceived in an exhibtion aquarium in Postojna cave in 2016 and the 21 surviving baby dragons became a global sensation. These days they are no longer quite babies, but it is possible to see them in small groups on exclusive tours with infrared lights in a special cave lab aquarium. My boyfriend and I got to see them and I must say that I was impressed by all the careful arrangements to ensure the animals were disturbed as little as possible during the visit.

You can of course see the adult human fish during the regular tour of Postojna cave in special dark aquariums, and in the Vivarium, an underground cave zoo (the above human fish video is from there, obviously taken with no flash). The Vivarium is located in one of the side passages of Postojna cave, where the walls are covered with visitor signatures from back when that wasn’t frowned upon. It’s partly a research biology lab and an exhibiton of various weird, icky cave critters. They’re fascinating in their own right, like this beetle that was the first officially confirmed cave dwelling animal, but I would prefer not to meet them in person. 🙂

Vivarium (underground cave zoo)

Phew! Guess what? We’ve made it to the end of this gigantic blog post. If you’ve read until here, you probably deserve a free ticket to Postojna cave. Unfortunately I can’t arrange that, but I do hope you enjoyed reading it and are now considering a visit to the Slovenian queen of the underworld.

Now, are there any cool caves in your part of the world? I am always looking for cave recommendations, because there’s just something about caves. 🙂 Let me know in the comments below.

P.S.: My boyfriend and I stayed at the fancy hotel Jama while visiting Postojna cave and you can check out my review of our stay here.