River Unica

The Unica is one of the most unusual rivers in Slovenia, a karst river that appears from underground, crosses a flat plain, and then vanishes underground again. It begins at the Planina Cave, Planinska jama, at the foot of a limestone cliff on the edge of Planinsko polje, in the Notranjska region of southwestern Slovenia. Inside the cave two underground rivers meet, the Pivka, which has already passed through the Postojna Cave system, and the Rak, which comes from the valley of Rakov Škocjan, and together they emerge into daylight as the Unica.

Outside the cave the river runs across the plain of Planinsko polje, a long flat-bottomed basin enclosed by wooded hills and limestone ridges. The river meanders through meadows and fields, with banks lined with willows and alders, and the water is clear and green. At the far end of the plain it disappears again, sinking into a series of ponors, or swallow holes, near the village of Laze, and from there it travels through the rock to reappear far to the north as the sources of the Ljubljanica at Vrhnika. The same water thus has several names and several lives, which is why the region is celebrated in the study of karst hydrology.

The plain also floods. In autumn and spring, when the ponors cannot swallow all the water, the polje fills and becomes a temporary lake, sometimes covering large areas of field and road. The flooding is part of the rhythm of local life, and the land is farmed and grazed in a way that allows for it. When the water recedes, it leaves meadows rich in flowers and a haven for birds, and between floods the area is one of the quietest and most pastoral in the region.

Paths and quiet roads follow the river, so walking and cycling are easy, and fishing and gentle paddling are possible when levels allow. The best viewpoints are around the cave entrance and the village of Planina, where remnants of medieval castles on the surrounding hills hint at the plain's long history. The area has few formal facilities, so bring water and food, and respect private land.

The Unica suits walkers, cyclists, birdwatchers, anglers and anyone curious about karst landscapes. It pairs naturally with Postojna Cave, Predjama Castle and Rakov Škocjan, which together illustrate the same underground water system. Check water levels and local conditions after heavy rain, when roads and paths on the plain can be under water.