On some distance near the entrance, the walls of the cave are completely black. This is not natural. During WWII, the Nazi had established a major airplane fuel depot in Postojna cave. They had sealed the entrance and it was heavily guarded. Nobody could come near from the front but the partisans in April 1944 succeeded in reaching the depot from behind, crawling into narrow passages that only locals speleologists knew. They blew up the depot that burned for seven days. The saboteur that set fire was taken by the blast, half burnt and wounded. His comrades thought he was dead and left. After two days when he had plenty of water to drink but no food, he succeeded finding a way out and escape both the cave and the Nazi patrols.
At the end of the tour of the cave there is a tank containing one Proteus Anguinus, a rather odd looking creature that is the shape of a snake with arms and legs, has no pigment, blind and didn't even appear to have eyes. The Proteus lives completely in the dark so I suppose it's irrelevant that it can't see. They only display a single specimen because the light would start harming them at some point, our guide said each one was only there for around a month before they found a different one to display.
It's nicknamed the "human fish" because it has three digits on it's arms and two on each leg and because it has gills, red in color.
They don't know how they reproduce, they can go for years without food and occasionally engage in cannibalism, odd little creatures indeed! I didn't take a picture of the actual one in the tank, I wasn't sure if the flash would bother it even further.
When in Postojna, you should try a local cheese dish called "Frigo" or "Frico" that is really, really good. I had it in an Italian trattoria at the Postojna cave site. It is a warm cheese and potato mixture, usually served with Polenta, that tastes incredibly good. Make sure you keep your eyes out for this culinary delight, you wont regret it!
If you take a bike ride around, or your car I guess, you will notice quaint little villages and beautiful houses full of flowers and lovely details.