Veternica is a cave located on Medvednica mountain in Zagreb, Croatia. At long, with a depth of and a vertical difference over , it is the longest known cave on its massif, and an estimated 6 km or more remain unexplored. In the 1960s, it briefly became the longest cave in Croatia. The first is available to visitors. In 2019, it had 5787 visitors. It is an archeological site where remains of several kinds of prehistoric animals as well as humans have been found. The cave has been protected by law since 7 July 1979, with registration as a Natural Monument on 11 July of that year.
The name Vetrenica is a Kajkavian -adjective formed from the reflex of Proto-Slavic "wind", to which the denominal suffix has been added. It is named for the wind that comes from the lower entrance of a cave as a result of temperature differences, except in the winter. Specifically in caves with two or more entrances and a significant difference in elevation between them. The upper entrance in this case seems to be a pit cave discovered in 1973 and named DvogaÃÂa, which sucks in warm external air in summer but emits relatively warm internal air in winter, opposite of Vetrenica.
Detailed descriptions of the cave itself can be found in Poljak 1934, BauÃÂià1945, Boà ¾iÃÂevià1960, ÃÂepelak 1977, ÃÂepelak 1979 and other sources.
The entrance is permanently dry, but Kramberger's guide relayed an account related to him by the father of his paternal uncle, the 60 year old Zolak Nacek, that Veternica had once flooded for 24 hours. In 2004, caver Vlado Boà ¾iàproposed that the entrance to the cave had been completely covered before this flood, which created the initial opening. This was dismissed by geologists SreÃÂko Boà ¾iÃÂeviàand Mladen Garaà ¡iàas a "fantasy", but defended by geologist Hrvoje Malinar, who took Boà ¾iàto evaluate the hypothesis in the cave on October 8th, finding multiple traces of an older flood in the main canal from the entrance to the stream, in addition to traces of high water level in the deeper parts of the cave where such levels had not been observed.
The wet part of the cave includes 14 active streams. Among other sources, these streams come from 9 known ponors, including 2 at Ponikve polje. The cave branches stretch towards these sinkholes, while the main channel runs 1250 m NNW towards Ponikve.
In 1960, Boà ¾iÃÂeviàdivided the cave into four sections:
The entrance to the cave was once only 45 cm wide and 29 cm high, requiring a prostrate entry; so unlike Velika peÃÂ na Rogu or the PeÃÂina Svetog Marka, it was not mentioned in printed literature until the regional onset of speleology, beginning with the account of Dragutin GorjanoviÃÂ-Kramberger in 1899. Word of the cave then spread with the works of .
An account of the first recorded entrance into the cave in February 1933 by Stanko Grà ¡etiàwith his brother and father was published on 8 March 1934 in the newspaper VeÃÂer, which popularised the cave and in the resulting exploration frenzy, the more accessible parts of the cave were quickly stripped of speleothems and the walls covered in names and dates of early explorers, as a 12 November 1934 article in VeÃÂer complained. In reaction, the Druà ¡tvo za poljepà ¡avanje Stenjevca secured the entrance and began requiring an entrance fee.
The first scientific exploration and mapping of the inside of the cave was made by and others in the spring of 1934, exploring the first 1488 m of passageway, as far as the Viktorija waterfall.
Entomologist Egon Pretner visited the cave in 1936, where he found the presence of Anophthalmus kaufmanni subsp. weingaertneri.
In the light of the Bombing of Zagreb, the Ministry of War of the Independent State of Croatia had ordered late in the year to explore the possibility of repurposing the cave as a storage shelter, but nothing came of it. In 1959, Hrvoje Malinar discovered 4 hand grenades and a German novel in Fraktur type, rheumatism oil and motorist or pilot goggles, all 1200 into the cave, evidently left by a German soldier.
Although not on the maps of the time, the cave had already been explored as far as the PVC siphon by 1945.
The cave entrance had become overgrown by 1947 when exploration resumed. The first geodetic map was drawn by a team of cavers in 1948, reaching as far as the PVC siphon and bringing the total length of the cave to just over 1590 m.
Apart from one shallow excavation by the Planinarsko druà ¡tvo "Prijatelj prirode" in 1940, the cave had remained untouched by paleontologists since 1934, but in 1949 the Planinarsko druà ¡tvo "à ½eljezniÃÂar" widened the entrance and built paths for visitors of the first section of the cave, discovering alongside Roman coins and other Bronze to Iron Age artefacts the skeletal remains of five recent individuals, which archaeologist Franjo IvanÃÂek speculated had been victims of BorÃÂec-born marauder Mijo BrezoviÃÂ, who was folklorically associated with the cave.
In 1951, following years of continued devastation by speleothem-hunters, the Commission for Veternica was formed, fixing a gate to the entrance and standing guard on Sunday for several years following to permit entry to visitors who paid for entry, though the 1951 gate was destroyed in 1955, and the 1969 gate was destroyed in 1970.
Systematic excavations began, led by Franjo IvanÃÂek and Vladimir MirosavljeviÃÂ, joined by Slavko Marjanac and Mirko Malez. Around the same time, Antun Markiàbegan systematically photographing the cave, the only previous attempts being those of Josip Poljak in his survey and of journalist Franjo Fuis published 20 April 1934 in Kulis. Concurrent with the archaeological and photographic documentation was an effort to map the entirety of the cave by SreÃÂko Boà ¾iÃÂeviàand Slavko Marjanac, which by 1955 had barely progressed beyond the stream, including one expedition involving the first bivouac in the SR Croatia; it was finally finished as far as the PVC siphon at the end of 1959.
The cave was visited by French speleologist Norbert Casteret on 12 March 1955, expressing surprise that the cave had not yet been equipped with electric lighting for tourism. After receiving approval, the cavers of Planinarsko druà ¡tvo "Zagreb", who had mostly transferred to the Planinarstvo druà ¡tvo "à ½eljezniÃÂar" and had begun visiting the cave almost weekly since 1950, built the first extensive paths for tourists under the leadership of professor Mirko Markulin.
In 1958, the Planinarsko Druà ¡tvo "Javor" conducted a flow trace experiment at the Ponor Jezeranca, 900 m from the ponor in Veternica as the crow flies, and the fluorescein soon arrived in the Bijela dvorana of Veternica, flowing from there to the Glavni siphon and later to the Dubravica spring in the valley several hundred meters south of the entrance to Veternica. When the green dye appeared in Gornji Stenjevec, it unsettled the village, so that the trace organiser Tomica Imenà ¡ek had to spend the entire day drinking green water to show it was not toxic. A further tracer experiment was conducted under SreÃÂko Boà ¾iÃÂeviàin 1969 with the same results, during which the dye took 8 hours to reach Veternica, indicating complex passages.
For decades, the cave remained unknown beyond the PVC siphon, but the Glavni siphon remained the most intriguing siphon. Following an 3 m dive and then on 21 June 1959 an 8 m dive by Hrvoje Malinar with a Drâger Aqua-Lung to a sandy bottom (the first freshwater cave scuba dive in SR Croatia), continued exploration was not deemed worth the risk, but Malinar had detected a narrow opening. Even with improvements in equipment, a 1988 dive by Branko Jalà ¾iàwas unsuccessful in progressing past the point reached by Malinar.
With the negative results of the dive and the remaining options for continuation growing increasingly difficult, the visits to the cave for exploration purposes by the original clubs decreased, and it became mostly a training cave for young cavers. One of their last notable contributions in this period came from Vlado Boà ¾iÃÂ, who finished the map to the PVC siphon in the 1960s on the basis of the work done in the previous decade. Where the à ½eljezniÃÂari left off, the Planinarsko druà ¡tvo SveuÃÂilià ¡ta "Velebit" began. In 1962âÂÂ1967, the Velebitaà ¡i under Hrvoje Malinar discovered the Velebitaà ¡ki kanal, Ponor 16 metara, Kanal iznad Limunove dvorane and the Kanal iznad Razruà ¡ene dvorane. These successes attracted some of the younger à ½eljezniÃÂari, who under the leadership of Boà ¾iàdiscovered much of the so-called "New Veternica" in 1964 (Kristalni kanal, Mlinarev rov, Velika dvorana). It was during this time that Drago PavliÃÂeviàproduced his series of photographs.
From 1966 on, explorations by the Velebitaà ¡i led by Malinar and Marijan ÃÂepelak mapped the Velebitaà ¡ki kanal to 562 m, AlpinistiÃÂki kanal to 501 m, Darijev kanal to 128 m and a number of smaller passages until the cumulative length of the new passages reached 2674 m. The new passages included: Ponor 16 metara dug to 68 m, Kukuà ¡ni kanal to 18 m, Kanal iznad Limunove dvorane to 85 m, Stari kanal to 85 m, "Nova Veternica" to 455 m, Aneks to 86 m, Kanal iznad Razruà ¡ene dvorane to 81 m and Kanal iznad Visoke dvorane to 24 m. The Pakleni kanal was discovered in 1969 after its strong airflow was detected. Digging to allow the passage of the shallow upstream PVC-siphon with a PVC tube in September 1977 led to the discovery of about 300 m of new passage to the already 5097 m long cave in the à ½eljezniÃÂarski kanal.
Though it was never the longest cave in the Dinarides thanks to the earlier exploration of Postojna Cave, it did eventually become the longest cave in SR Croatia. In 1973, JopiÃÂeva à ¡pilja - Bent system surpassed Veternica as the longest cave in SR Croatia, with a length of 6247 m against Veternica's 5994 m. Veternica would eventually catch up but not before being surpassed in length by other caves. On 20 November 1983, shortly after an expansion of JopiÃÂeva à ¡pilja in the summer, the Panjkov ponor - VariÃÂakova à ¡pilja system surpassed it as the longest cave in SR Croatia, ending competition between Veternica and Panjkov ponor, only to be surpassed itself as such on 1 September 1984 by the ÃÂulin ponor - Medvedica system.
With further exploration of the à ½eljezniÃÂarski kanal, June 1979 saw the total length of the cave reach 5996 m. A map of the cave finished in 1979 was published by ÃÂepelak in 1980, though by the time of its publication it was already out of date, thanks to about 70 m of newly discovered passage in the à ½eljezniÃÂarski kanal. Continued exploration brought the total length of the cave to 6576 m. This was due to the discovery of new passages beyond "New Veternica" in the autumn of 1984. First, Robert Dado scaled 9 m of muddy cliff with pitons on October 14th. Using those pitons, Svjetlan Hudec was able to climb a further 9 m up the same cliff on November 3rd, at the top of which was the largest chamber in the cave, named Markulinova dvorana.
Removing sediment with a hoe, the Velebitaà ¡i found a continuation of the Zadnji kanal. Then in several expeditions beyond the Prolaz motike, 113 m of canal were explored, so that the total length of the cave at the beginning of 1992 was 6767 m. Although no further explorations were , several hundred meters further were explored by 1999, for a cumulative length of 7128 m.
In 1977, the systematic preparation of the cave for tourism began, during which more than 860 graffitos were erased and the cave was electrified as far as Kalvarija. But already in 1978 the funding dried up thanks to the economic crisis in the SFRJ, and so the cave was not ready to accept tourists until 1979. Malinar trained the first tour guides from among the cavers of Zagreb in 1978, and these guides began to provide tours beginning in April 1979, several months before the legal designation of the cave as a Protected Natural Monument. At first, guides rotated, but already in 1979 the Damir Prelovec became its sole guide, replaced in 1980 by Juraj PosariÃÂ, who remained in that role until the transfer of the cave to the Nature Park Medvednica in 2000.
After control was transferred to the Javna ustanova Park prirode Medvednica, the cave was closed to tourists and restricted to training cavers for several years, reopening to tourists in 2002, but with effective restrictions on caver activity by Nives Farkaà ¡-Topolnik after she was named its first rector due to differences of opinion on the importance of exploration. But some work was allowed to continue until a 2020 document by the new rector Marina Popijaàrestricted the maximum caving time to 6 hours on 1 day of the month, making exploration trips impossible. The Commission for Speleology of the Croatian Mountaineering Association confronted the park administration about it in a 2021 meeting, but their concerns were dismissed on the grounds of the results of an internal investigation on improper behaviour in the cave by members of an unnamed organisation, and declined to comment on the reasons for their restrictions upon a request from the editors of the Speleolog magazine.
The only notable steps towards exploration by cavers since the takeover were the 2009 laser telemetry of the main part of the cave from the entrance to the PVC siphon, providing greater vertical accuracy; and the discovery of a new chimney inside Markulinova dvorana in 2012, alongside a few other minor passages.
The temperature in the cave is roughly 10ðC year-round.
The radon concentration was measured in 2024 at various locations throughout the tourist section of the cave, with an average of 7394ñ104 Bq/m<sup>3</sup>, and a maximum of 7542 Bq/m<sup>3</sup> at the Koncertna chamber, which following the annual dose limit guideline of 20 mSv/year limits tour guides to 400 hours per year.
As of 1977, water was known to run through 36% of the cave. The ponors of the Jaruga doline drain into the Velebitaà ¡ki kanal and the Pakleni kanal, which also receives water from the southern end of the Staglià ¡ÃÂe doline. The northern end of the Staglià ¡ÃÂe doline drains into the deeper parts of Vetrenica, which also receives water from the Ponikve polje.
One of the three largest streams in Veternica enters through the AlpinistiÃÂki kanal. A smaller stream flows through th Kanal iznad Razruà ¡ene dvorane.
In the 1970s, an experiment was conducted during which the Stream 13 was rerouted into the Fosilna dvorana.
As of 1977, 53.2% of the cave was in dolostone, the rest being at the dolostone-limestone contact or in limestone. There is some breccia and conglomerate at the end of Stari kanal, likely near contact with limestone.
Paleomagnetic analysis of fossil stream sediments has placed the lower boundary for the formation of the cave at the BrunhesâÂÂMatuyama reversal. The initial formation of the cave following the uplift of the ground above it ought to have been mostly phreatic on morphological grounds, although no dates have been produced from this period yet.
One stalactite caked in stream sediment at 680 m from the entrance was U-Th dated to about 640 ka BP, providing evidence for a vadose phase predating the second, partially phreatic phase. The oldest flowstone tested dates to 550 ka BP, before the formation of the paleolake. As the uplift continued, the mouth of the cave would have risen above the water level, leading to the formation of lower springs similar to Dubravica. This mostly vadose phase would have included subterranean lakes.
Much of the formation of Veternica formed in conditions at least about 380 ka BP at the unconformable contact between Miocene marly limestone and underlying Triassic dolostone, as a largely phreatic subterranean paleolake 475 m upstream inside the cave. It was during this period that the shelfstones in Majmunski prolaz at about 450 m from the entrance formed. Sediment buildup blocking lower springs is proposed as the reason for the water level rise that allowed for phreatic conditions to dominate. The water level of the paleolake declined only slightly during this period, despite leaving 9 different shelfstone levels.
Between about 245 and 235 ka BP, the system experienced a geologically rapid water level drop, as evidenced by the transition from shelfstone to flowstone. It has been suggested that this water table fall was due to the ~350 m tectonic uplift along the southern flanks of Medvednica in the Quaternary, which could also explain the recession of the main stream from the siphons Ponor 16 metara and Kukuà ¡ni to Glavni. On the evidence of the flowstone in the Velebitaà ¡ki kanal, the subterranean water level must have fallen by at least 6 m. Following this event, the Stone Waterfall () flowstone formation at about 250 m from the entrance began forming about 212 ka BP and continued to about 205 ka BP, as the result of paleowater flow from the Velebitaà ¡ki channel. By the end of its formation, the water level had fallen by a total of about 14 m since the final phase of shelfstone formation.
After hydrological activity ceased at the end of the Riss glaciation, the oldest clastic sediments at the cave entrance were deposited. This corresponds to layer K; layer J was deposited during the Riss-Würm interglacial (MIS 5e, 130-115 ka BP); layers I-D were deposited during the Würm glaciation, of which I-H from MIS 5 to MIS 3, 115-40 ka BP
The fifth layer of the chamber at the entrance was formed in a single catastrophic erosion episode that covered the entire entrance, following which all mammalian habitation of the cave seems to have ceased. This is layer G. It has been connected to the colder conditions during MIS 4, 71-57 ka BP; or one of the colder phases of MIS 3, 57-29 ka BP, which would match layers F and E which are dated to MIS 3, 40-30 ka BP.
Layer D was deposited during mostly after the Last Glacial Maximum during MIS 2, 29-14 ka BP. Layer C is a calcite cap that formed at the transition from the Pleistocene to the Holocene. layer B and the humus layer A formed in the Holocene.
Layers H, I and J contain artefacts belonging to the Mousterian culture. At least layers I and J are beyond the limits of <sup>14</sup>C dating. Only layers H-I yielded bone implements, including 33 knapping bones, of which 13 were fashioned from the bones of Ursus spelaeus, which is a record for the Middle Paleolithic. As of 2020, more than 500 stone artefacts have been unearthed at Veternica, of which 46% quartz and 28% chert.
In 1956, the discovery of a human skull believed at the time to be around 150,000 years old was published, prompting a number of prominent anthropologists to visit Zagreb, including Hallam L. Movius, Germaine Henri-Martin, , SreÃÂko Brodar, Boà ¾o à  kerlj, Branko Gavela and others. This skull, from layer H, turned out to be that of an anatomically modern human, the depth being explained as by burial practices. The remains were radiocarbon dated to the Roman period in 2024.
9 Mousterian fire pits were discovered from 1955 on: 2 in front of the cave and the rest in the entrance chamber. One of the charcoal samples is too old for <sup>14</sup>C dating, with a minimum result of 50 ka BP.
In layer F, several stone implement fragments were discovered, which Malez assigned to the Aurignacian solely on stratigraphic grounds, but thanks to these implements being mixed with the Mousterian implements, it was not possible to identify them during a verification attempt. The same applies to the chert and quartz implements discovered in layer D, although layer D also included one fire pit. Layer D also contained 4 skulls, of which 3 together with 1 femur and scattered U. spelaeus bones beneath a stone slab, one of which had cut marks.
Among the more recent finds are 3rd century Roman coins, a bronze fibula. These and a number of ceramic artefacts from the Neolithic through Late antiquity were found in layers B and A, of which none in layer A predate the Iron Age; though several finds from antiquity were found beneath layer C. At the very end of the NW passage, there was a walled Neolithic graveyard with strewn human bones, including whole and fragmentary skulls, all belonging to young individuals, some of whom were children. Also in the NW passage, layer B yielded a human skull, which because of association with Bronze implements was dated to the Bronze Age. During excavations in 2015-2016, human remains were founded that dated to the 3rd-4th centuries, together with a Roman coin and a bronze needle.
The skull of a modern human was unearthed near the entrance in 2002 by a team led by Nikola VukosavljeviÃÂ. The skeletal remains of five recent individuals (three males, one woman and one child) unearthed in 1949 were likewise found near the entrance.
As of 2024, all human remains found within the cave have been dated or redated to the Roman period: S2 to AD 127âÂÂ250, S6 to AD 218âÂÂ365, S4 to AD 224âÂÂ556, S3 to AD 243âÂÂ353, VETPN<sub>5</sub> to AD 336âÂÂ440, and VET<sub>15</sub>SJ<sub>104</sub>K6 to AD 419âÂÂ598. The radiocarbon dating of S1 failed.
Fossils of Lithothamnion algae have been found, responsible for the upper layer of the cave.
In 1955, a complete Ursus spelaeus skeleton was unearthed, its presence having been known since 1934, comprising 75% of all animal bones, and even more in layers E and F, reaching 99% in F. This was in addition to a number of Panthera spelaea bones, and teeth of Castor fiber and Marmota marmota. The remaining species included Canis lupus lupus, Capra ibex, and Sus scrofa.
The remaining species include: Alces alces, Bison priscus, Capreolus capreolus, Cervus elaphus hippelaphus, Cricetus sp., Cuon alpinus, Felis silvestris, Hystrix sp., Lepus europaeus, Martes foina, Martes martes, Meles meles Mustela erminea, Mustela putorius, Panthera pardus, Rupicapra rupicapra, Stephanorhinus sp., Ursus arctos arctos, Vulpes vulpes, and others.
The Crocuta spelaea specimen found in layer F remains unconfirmed.
18 species of bat have been recorded in Veternica, of which 12 regularly hibernate in the cave. It is inhabited year-round by small numbers of Rhinolophus ferrumequinum; for winter hybernation by colonies of Myotis emarginatus, Rhinolophus hipposideros, and R. ferrumequinum; and in summer by R. euryale and R. mehelyi.
The bat population was discovered to be in decline in 2003. To protect the bats, winter visits to the cave were banned in 2004, and a bat-friendly gate was put in place in 2005. In January 2019, the R. hipposideros population consisted of 1290 individuals, but after 15 years of constistant growth a drop to 528 individuals in January 2021 was noticed. Over the next three winters, the population continued to decline.
It is the only known locality for Pseudosinella dallaii , described at this site.
It is one of only 2 locations recorded for the Medvednica endemic Anophthalmus kaufmanni subsp. weingaertneri .
In 1988, a Chthonius specimen collected by Branko Jalà ¾iàwas described as Chthonius raridentatus, though in 2014 this was shown to be Chthonius raridentatus .
Other invertebrates include Eukoenenia sp., Heteromurus nitidus , Lithobius sp., Mesoniscus graniger , Niphargus likanus , Plusiocampa cf. nivea , Rhagidia sp., Schubartia lohmanderi , Scoliopteryx libatrix , Troglohyphantes excavatus , Troglophilus cavicola .
The Veternica cave is home to at least 47 protist species. The highest diversity (36 species) and abundance (>500 individuals/mL) is found in those sinter pools richest in bat guano. The most widespread protist is Euglypha laevis . Sphatidium sp. are only found in clay pools. A. rotundata is restricted to a habitat.
Amoebozoa include the Veternica endemic Centropyxis bipilata and a number of other species: Arcella artocrea , A. rotundata , Centropyxis aculeata , C. aerophila , C. constricta , C. elongata , C. laevigata , C. plagiostoma , Cochliopodium sp., Cryptodifflugia oviformis , C. pusilla , C. sacculus , Cyclopyxis eurystoma , Cyphoderia ampulla , Difflugia oblonga , D. cf. pristis , Diplochlamys sp., Diplophrys sp., Euglypha bryophila , E. laevis , E. rotunda , E. tuberculata , cf. Flamella sp., Frenzelina sp., Heleopera sp., Korotnevella sp., Mayorella sp., Microchlamys patella , Microcometes paludosa , Plagiopyxis declivis , Pyxidicula sp., Rhizamoeba sp., Tracheleuglypha dentata , and Trinema lineare , T. enchelys , Vahlkampfia sp., Vanella sp.
Heliozoa include Acanthocystis myriospina and Raphidocystis marginata .
Ciliophora include Cinetochilum margaritaceum , Colpoda steini , Cyclidium glaucoma , Euplotes sp., Glaucoma sp., Litonotus lamella , Nassulida sp., Pleuronema sp., Pyxicola sp., Sphatidium sp., Vorticella sp.
The cave is also home to the Stramenopiles species Actinophrys sol and the Heterotrophic Flagellate species Peranema trichophorum .