24,120 meters of subterranean tunnels of the Postojnska jama cave system have been explored until the year 2022. This karst cave system with a maximum documented depth of 115 meters near Postojna is the second-longest in Slovenia after the M16 system - Tolmiski Migovec, which has a length of underground tunnels of 43,009 meters and the largest tourist cave on the Dinaric Karst.
The cave system of Postonjska jama also includes its natural and historical entrances: Otoška jama, Magdalena jama, Črna jama and jama Pivka. The cave was created by a subteranean river Pivka, which sinks from the Postojna polje under the hill Sovič and continues its underground flow towards the underground confluence with the river Rak in the Planina jama cave.
Formation of a multi-level cave system
After the Pivka river made its way underground, it gradually lowered its bed over the course of two million years, creating different levels of the cave. The water that seeped through the bejeweled surface deposited calcite drop by drop in the dry tunnels from the dissolved limestone, creating unique stalactite forms.
The constant temperature inside the cave three decades ago was about 8 °C, but today it varies between 8 and 10 °C, which is a result of global climate change.
The cradle of speleobiology
Postonjska jama cave is famous nowadays as the cradle of speleobiology. The most famous is the Olm (Proteus anguinus). In 1797, Josip Jeršinovič the noble Löwengreif discovered it in Črna jama. In 2016, the reproduction of a human fish in captivity was successful in Postojna Cave for the first time in a tourist cave.
In 1831, the first cave beetle was discovered in Postonjska jama, "Dobrovratnik" (Leptodirus hochenwarti). Today, the Postojna–Planina cave system is known to host over 175 animal species, including 115 true troglobionts, the highest number recorded in any single cave system worldwide.
Traces of human presence and wartime history
The oldest signatures on the cave walls date back to the 13th century. Organized tourist development began after 1818, when Luka Čeč discovered the inner parts of the cave. In 1884, electric arc lighting was introduced, among the first in the world.
During World War II, German forces stored fuel inside the cave. On April 23, 1944, a sabotage unit of the Vojkova Brigade managed to infiltrate through an old tunnel from Črna Cave and blow up the depot. The fire burned for a week, and soot is still visible today.
Documenting the cave – a personal perspective
Postojna Cave has been an important part of my research and documentary work. I first documented the entire cave system in 1999, creating a comprehensive visual record. My most recent full documentation was completed in 2012, using advanced techniques to update the archive.
Literature: Kataster jam (2022); Skoberne, P.: One hundred natural sights of Slovenia (1988).