More than 11,500 caves and sink-holes are known in Croatia, on the mainland, on the islands, underneath the sea, along rivers, in the mountains.
There are still many areas on which no systematic speleological research has been carried out. It is rightly assumed that their number is much greater since many of them d not have natural entry points on the surface and are discovered exclusively thanks to construction works.
For instance, in the course of the construction of highways, bridges, tunnels and viaducts, more than 1,000 caves and sink-holes have been discovered in Croatia that do not have openings on the surface. When it comes to the number of discovered and researched caverns, Croatia is number one in the world. Croatian speleologists are very important figures in the World Speleological Union (Unio Internationale de Speleologie – UIS).
The specific cave erosion, corrosion and icicle forms (speleothems – stalactites, stalagmites, stalagnates, helektites, botroids, conolites and others.), endemic animal species (the olm – “human fish”), special underground species of underground fresh-water sponge, underground leeches, underground crabs, etc.), significant archaeological and paleontological findings – all of these are postcards of the cave environment, an independent eco-system protected from the sun, which flourishes underground, and is available only to speleologists.
The Croatian karst underground is filled with such cave oases of “centuries-old karst shades”, which can be offered to visitors as a form of vacation under-ground. Only a relatively small number of caves can accommodate real tourists, as not many have been specifically adjusted for such tours.
Paths, guides and lighting for tourists exist in the upper and lower Cerovac caves near Gračaci, cave Veternica near Kotlenice on the northern base of Mountain Mosor, Grgos caves near Samobor, cave Vrlovka near Ozalj, Barač caves near Rakovia, Samograd caves near Perušić, cave Biserujka near Dobrinje on the island of Krk, sink-hole Baredine near Poreč, cave Mramornica near Brtonigla in Istria, cave Feštinsko kraljevstvo near Žminj in Istria, Đurović cave in Ćilipi near Dubrovnik. Especially attractive is the Modra špilja (“blue cave”) on the island of Biševo that can only be visited via boat.
Some caves, apart from their beauty, have additional interesting tourist attractions. For instance in cave Veternica, one can find traces and remains of the died-out bear, and in others one can see fossils, bats, etc; in the Đurović cave beneath the Dubrovnik airport, indigenous wine sorts are exhibited, and the Modra cave on the island of Biševo is rich in natural lighting effects (reflexive blue lights in the sea-water).
In cave Baredine, the only cave accommodated for tourists in Croatia, the “human fish” (olm) is exhibited in its natural environment…