Welcome to Postojna
The cave has been known – and visited – by residents of the area for centuries (you need only look at Passage of New Signatures inside the Vivarium Proteus). But people in the Middle Ages knew only the entrances; the inner parts were not explored until April 1818, just days before Habsburg Emperor Franz I (r 1792–1835) came to visit. The following year the Cave Commission accepted its first organised tour group, including Archduke Ferdinand, and Postojna’s future as a tourist destination was sealed.
Since then more than 36 million people have visited it (with some 6000 a day in August; rainy summer days bring the biggest crowds). It's a big, slick complex – and it doesn't come cheap (beginning with a €4 charge for parking).