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.

Unica
Unica flows out of the cave
Location
Country	Slovenia
Physical characteristics
Source
• location	Underground confluence of the Pivka and the Rak in Planina Cave
• coordinates	45°49′11.17″N 14°14′46.51″E / 45.8197694°N 14.2462528°E / 45.8197694; 14.2462528
• elevation	500 m (1,600 ft)
Mouth
• location	Ljubljanica near Vrhnika
• elevation	308 m (1,010 ft) (underground)[1]
Length	20 km (12 mi)
Discharge
• average	13 m3/s (460 cu ft/s) (at the source in Planina Cave), 24 m3/s (850 cu ft/s) (at the outflow in Vrhnika)
Basin features
Progression	Ljubljanica→ Sava→ Danube→ Black Sea