Pivka Cave and The Black Cave

These two caves are part of the Postojna Cave System and at the same time the last two caves through which the underground river Pivka flows before finally disappearing, only to appear again in Planina Cave. A characteristic of both these cases is that they are entered from the surface through a collapse doline – a karst feature formed by the collapse of part of a cave ceiling. The caves are connected to each other by a man-made tunnel just over 100 metres long.