Europe,  Slovenia

Visiting the Postojna Caves

The Postojna Caves are one of the biggest and most impressive show caves in the world. They are situated about a 45 minute drive south west of Slovenia’s capital, Ljubljana and have been visited by an estimated 37 million people since they opened about 200 years ago. That seemed like a good enough reason for us to pay a visit ourselves.

Slovenia Postojna Caves Stalactites Stalagmites

Karst Landscape

Another good reason is that caves are one of the most important features of the landscape in this area and so we thought we should learn more about them.  The geology of this part of Europe is dominated by limestone, which has weathered over millions of years to form what is now referred to as a karst landscape. This landscape features underground rivers, sinkholes and caves with stalactites and stalagmites and many of these caves are open to the public.

Exciting Train Ride

We looked at the different caves you could tour and particularly chose Postojna as it is the only one with a train running through it and we thought that looked like a lot of fun – and it didn’t disappoint!

All visitors are taken on a guided tour and throughout the peak season (May to October) these run every hour on the hour. Outside the cave entrance, you are grouped by language and then led into the underground train station. There were two narrow gauge trains standing next to each other and we couldn’t believe how long they were: they must carry hundreds of passengers at a time into the caves.

We were amazed at the length of the trains that take you underground – they must transport hundreds of people at a time into the caves!

The seats and the trains reminded us of the sort of carriages you sit in for many of the rides at Disney, only without the safety rail that usually comes down across your lap, which all added to the fun and excitement of the visit. The journey starts with a thrilling ride in the dark through narrow, low ceilinged tunnels where in places we felt like we needed to duck down as we passed through. You are warned not to stand up but there is nothing stopping you from doing so, except the knowledge that you would probably decapitate yourself if you did! You then emerge into the caverns themselves and watch in awe as you travel past mile after mile of incredible features, the most impressive of which are carefully lit so that you can see them properly in the semi-darkness.

Slovenia Postojna Caves train ride
The train ride through the first few kilometres of galleries and caves was great fun.

It takes about 10 minutes to travel the 3.7km to the end of the line, deep within the caves, and from here you proceed on foot, heading further underground. So far, 24km of underground passages, galleries and halls have been discovered at Postojna, of which 5km are open to the public.

Walking Tour

The walking section of the tour covers about another 1.5km and takes you up and down through more amazing caverns and galleries. There are no stairs, but in places the path is pretty steep. It is damp too, but amazingly the floor wasn’t slippy. At several points, the tour guide identified where visitors could take a shorter tour if they were struggling with the walk or you could just return directly by train without doing the section on foot at all. The guide stopped at several places to point out different features and explain how they were formed, which was interesting, without being too technical or too long. However, you really needed to keep up with him: there were speakers in the cave to help people hear what was being said, but it was a big group and on a couple of occasions we missed some or all of what was said.

Slovenia Postojna Caves guided tour
Hopefully from these images you can get an idea of the sheer size of the caves you visit at Postojna

How the Incredible Cave Features Form

Our guide explained that most of the features in the cave were formed by rainwater passing through the limestone rock and dripping into the cave. They are called speleothem, from the Greek word ‘spelaion’ meaning cave and ‘thema’ meaning deposit, the most common of which I think everyone has heard of: stalactites and stalagmites.

Slovenia Postojna Caves Pillars Stalagmites Stalactites
Some of the impressive pillars and stalagmites in the Postojna Caves. It is hard to get your head around how long these structures have taken to form – on average they grow at a rate of 1cm per century.

At the surface, rainwater mixes with carbon dioxide in the air and soil/plants to form a weak carbonic acid. As this acid passes through fissures and cracks in the limestone (which is made up of calcium carbonate) it dissolves the calcium in the rock and eventually this calcium-rich water drips into the cave. Here the water evaporates, leaving behind a tiny amount of calcite on the ceiling of the cave. Slowly over time this calcite builds up, forming icicle-like spikes that hang from the ceiling (stalactites). Where the water drips onto the floor of the cave, the calcite can build up to form stalagmites. When these two features eventually meet in the middle, a pillar is formed. Some of the most beautiful formations occur when water drips down the ceiling or wall of a cave and the calcite is deposited in a thin, almost translucent, sheet.

Slovenia Postojna Caves Stalactites
Left: some of the incredibly beautiful curtain stalactites. Right: others looked like the pipes of a church organ

As we gazed at the huge stalactites and stalagmites, our guide told us that they grow at a rate of about 1cm every century and we began to understand just how long this cave and its incredible features had taken to form. Some of the speleothems are different colours, caused by other minerals in the limestone. Where iron is present, they take on an orange appearance; where aluminium oxide is present, they appear black.

Astonishing Diversity

One of the amazing things about the Postojna Caves is the huge diversity of different karst formations that exist there. For me, the most beautiful were the wavy curtain-like formations, but there were others that looked Iike icicles, some like the pipes of a church organ and in one cavern the ceiling was completely covered with thin spaghetti-like stalactites, which looked eerily beautiful. Some were narrow and thin, others fatter and irregularly shaped with bulges, which we would later learn was to do with fluctuations in the amount of carbon dioxide and water at different times. One of the most famous formations at Postojna is the 5 metre high, snow-white stalagmite known as ‘Brilliant’ that is over 100,000 years old.

Slovenia Postojna Caves Brilliant stalagmite
Left: the extensive cave complex at Postojna. Right: one of its most famous stalagmites, called Brilliant.

Sheer Size

But for us, the most impressive part of the whole visit was the sheer size of Postojna. “I can’t believe how BIG it is!” the we kept saying. The network of caves, galleries and tunnels seems to go on forever creating a breathtaking underground landscape. It was virtually impossible to capture with a camera the immense size and other-worldly beauty of it all and I fear that most of our photographs don’t really do it justice.

Slovenia Postojna Caves huge gallery
It is hard in a photograph to capture the size and beauty of the caves. You can just make out on the right of this picture where the steps are leading people down into another vast gallery

Still Active

It really is hard to get your head around the time spans involved. We learnt that the caves we were standing in were carved out some 2 million years ago by an underground river and that the Postojna cave complex is still being formed. At a lower level, the Pivka River was still gushing underground, actively eroding the limestone away and creating new caves beneath our feet.  At the end of the tour you get to see this active part of the cave system and outside you can see where the river disappers underground.

Slovenia Postojna Caves Pivka River
The Pivka River is still carving out the limestone below where today’s show caves are situated. At the end of the tour you get to see (and hear) it as it roars through one of the newer caves it is creating. Outside you can see where it disappears underground

At the end of the walking part of the tour, you return to the underground station for the reverse journey back out of the cave system, so you get a second chance to marvel at the incredible features as you pass. Some people say that the train is a bit showy and tacky, but we thought it was great fun. And because you travel so far underground (a lot further than you could explore on foot alone), you really appreciate just how vast these caves are.

Other things to do at Postojna

After you have toured the caves, there are two other things to see at Postojna: the Vivarium and the Expo.


This is a small museum in one of the caves where you can see and learn all about the proteus or ‘human fish’ that live in the caves.  Proteus can live for up to 100 years and they feed on things like cave shrimp, worms and snails, but they can survive for several years without food. At 25-30cm long, the proteus is the largest of all cave dwelling animals and is similar to a salamander or newt. Because it lives in complete darkness, it has no need for protective skin pigments and so is a pale pinky-white colour and, although proteus are born with eyes, these atrophy as they grow since they have no use for them. Instead, their senses of touch, smell and taste are more highly developed and they have a very sensitive inner ear. Proteus live in water and have external gills that look like red tufts on either side of their head.

Slovenia Postojna Cave Vivarium Proteus Olm
Inside the Vivarium we learnt about the different creatures that inhabit the caves, especially the famous Proteus or Olm

In the Vivarium we also saw and learnt about other strange and fascinating cave dwellers like cave crickets, cave beetles (can you believe there are over 2000 species of cave beetles, many of which have not been fully described and categorised yet!), woodlice, spiders, tiny snails just 2-3mm long and cave shrimp. Similar to the proteus, many of these have atrophied eyes and their other senses are more highly developed than those of their surface counterparts.


The Expo at Postojna is a well designed, hands-on space that covers the history of the caves and the geology of karst regions like this one. However, despite the caves themselves being really busy, we were the only people in there, which seemed a shame as there were lots of interesting things to see and learn. The girls loved one section where you could alter the levels of carbon dioxide and water entering a cave and see how it affected the development of the stalactites and stalagmites. Then there was another section where you could measure your height and find out how many years you would’ve taken to grow if you were a stalagmite. Based on the fact that stalagmites grow approximately 1mm every 10 years, we found out that E would’ve been 15,200 years old by now!

We had fun in the Expo at the caves where there were lots of hands-on exhibits. We learned about how karst features were formed and could see how people travelled into the caves in days gone by

There were also exhibits relating to the history of tourism at Postojna, which opened to visitors in 1819. You could see one of the old seats in which visitors used to tour the caves, pushed along by a guide, as well as some of the old lighting and other equipment that was used. The caves were such a popular attraction that electric light was installed in them in 1884, several years before it was available in Ljubljana itself. They also had a cab and carriages of one of the trains and you could stand in the cab watching a screen in front of you and see what it was like to drive it through the tunnels and caves.

We had the Expo almost to ourselves

We thoroughly enjoyed our visit to Postojna Caves – it provided a great mix of fun, education and awe-inspiring nature – what more could you want from a day out?!  The girls thought the train ride was cool, but they also loved playing with the interactive exhibits in the Expo.

Practical tips for visiting the Postojna Caves:

  • Wear or bring some warm clothes. You spend an hour and a half inside the caves and it is only about 10 degrees Celsius in there.
  • Leave yourself plenty of time. As well as the tour of the caves, there are the Vivarium and the excellent Expo to explore where you will learn so much more about the caves you have just seen.
  • The tour doesn’t involve steps, but the path through the caves is very steep in places. If you can’t manage the walk, you can still do the train ride though – at a couple of points during the walking part of the tour there were opportunities for people who were struggling to take a shorter tour or go back directly to the train.
  • You ARE allowed to take photographs in the caves, but you are not allowed to use flash or tripod.
  • From the start of May to the end of September, there are tours every hour on the hour, which is worth bearing in mind when timing your visit so that you don’t have to wait too long. In other months they are less frequent – check the website for more information.
  • You can also book your tickets (and choose the time of your tour) online, which would be advisable during the peak season when some of the more popular times book up early. I just looked ahead for June and many of the 10am and 11am tours were fully booked.
  • The guided tours are done in four to six languages, with many more available via an audio guide.
  • There is a large restaurant at the site if you need to stop for refreshments, and some good toilet facilities.
  • There are also a number of souvenir shops, including one underground near where you board the train for the return journey.


  • Liz Wetherby

    What a great day! Those formations in the caves are absolutely breathtaking! How cool that they had the Expo for the girls. When I saw they had opened the cave to visitors almost 200 years ago I was amazed. The Vivarium was fascinating. I’ve never heard of such creatures. Amazing how they adapt to their environment. Thanks for taking along on this wonderful day trip!