A Planinska jama az egyik leghosszabb szlovén barlang. A barlang bejáratától 500 méterre két földalatti folyó találkozik. A képeslap Dr. Lénárt László gyűjteményébe tartozik.

The Cave Mountain (Slovenian: Planinska jama), formerly also Little Castle Cave (Little Castle Cave) after Little Castle in the vicinity of its entrance, is one of the longest Slovenian water caves. It is a huge tunnel and the subterranean bed of the Unica River. It is located in Inner Carniola. Five hundred meters from the entrance to the cave is the confluence of two underground streams: the Pivka River, flowing from Postojna Polje through Postojna Cave, and the Rak River, flowing to Planina Cave through Weaver Cave from Rak Škocjan. This is one of the largest confluences of subterranean rivers in Europe.