Pivka Valley is part of Slovenian kras, a unique limestone geological area, marked by underground rivers, intermittent lakes and rivers, and numerous caves. Postojna Cave and Škocjan Cave are the largest and most accessible, attracting an unending stream of visitors. Pivka river emerges in Zagorje, flows partly on the surface, partly underground along the Pivka Valley, depending on the season and the rainfall, disappears underground into Postojna cave system, to reappear as Unica in the Planinsko polje, there continuing its performance as vanishing river and occasionally as a lake.
Pivka valley and Planinsko polje are well worth a visit. This is a karst region of unspoilt beauty and unique natural phenomena.