The term karst applies to areas built of water-soluble rocks, where erosional and corrosional activity of water created underground cavities and caves accompanied by superficial karst phenomena (sinkholes, canyons, karren etc.)

Pseudokarst caves are usually formed by mechanical processes, and are conditional on tectonic structure and waterproofness of the rockc. These caverns could be very large and we can determine several various types of them according to their origin, e.g., joint caves, layer caves, collapsed caves etc. The Geopark features a number of pseudokarst caves, especially in less resistant quartzose sandstones. Many of them reach considerable sizes (Postojna, Ludmilina, Sklepy). In the past, they were often used as dwellings by cave people, and their sedimentary fill contains archeologically significant contents.

Hollows in quartzose sandstones were often used by man as dwellings, or at least as sheds and stables for livestock.