Postojna Cave

Postojna Cave (Slovene: Postojnska jama; German: Adelsberger Grotte; Italian: Grotte di Postumia) is a 24,340 m long karst cave system near Postojna, southwestern Slovenia. It is the second-longest cave system in the country (following the Migovec System) as well as one of its top tourism sites. The caves were created by the Pivka River.

The Pivka is a karst lost river in Slovenia. The river is 27 kilometres (17 mi) in length. The Pivka ends in Planina Cave, where it merges with the Rak River and then the Unica River. The confluence of the Pivka and the Rak is one of the largest subterranean confluences in Europe. The Pivka created Postojna Cave, the longest cave system in Slovenia as well as one of its top tourism sites.