Planina Cave

It is a huge tunnel and the subterranean bed of the Unica River.

Five hundred meters from the entrance into the cave is a confluence of two underground rivers: the Pivka River, flowing from the 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.

[1] Entrance into the cave is at the southwestern part of Planina Polje in the gable end valley below 65 high rocks.

The length of the joint system would be over 31 kilometres (19 mi).