Postojna Cave

Postojna Cave, in southwestern Slovenia, is a karst cave system stretching over 24 kilometres, carved by the Pivka River over an estimated two million years. It has been a tourist destination since at least the early 19th century — visitors have left graffiti dating back to 1213, and the cave was wired with electric lighting as early as 1884, before many European cities, and today visitors travel through part of the cave by an underground railway first installed in 1872.

The cave is the type locality for the olm (Proteus anguinus), a pale, blind, aquatic salamander that can grow over 30 centimetres long and live for over a century, almost entirely without food for years at a time, in the total darkness of underground rivers across the Dinaric karst. When occasional flooding washed olms out of cave systems and into springs, local people who had no knowledge of the cave system above — and who had certainly never seen anything resembling the creature before — interpreted the pale, serpentine animals as the offspring of dragons believed to live in the depths of the earth, a belief recorded by the 17th-century Slovenian polymath Johann Weikhard von Valvasor. The species was given its scientific description in 1768 by Josephus Nicolaus Laurenti, who classified it (inaccurately, as later genetic studies confirmed it is a true salamander rather than anything closer to a fish or reptile) based on the handful of specimens then known, and the olm remains a flagship species for cave conservation in the region, with a dedicated breeding and research facility, Vivarium Proteus, operating within the Postojna cave system today.