The Unica is a river in Slovenia. It starts as the underground confluence[2] of the Pivka and the Rak in Planinska jama. This is the largest confluence of underground rivers in Europe. 300 meters (980 ft) further, the Unica emerges near Planina. It flows north through the Planina Karst Field (Planinsko Polje) through the municipalities of Postojna, Cerknica, and Logatec, where it returns underground.[3] It then flows for about another 10 kilometers (6.2 mi) underground, emerging 142 meters (466 ft) lower[1] at multiple springs near Vrhnika to form the Ljubljanica River.