The Pannonian Sea stretched 12 million years ago in the area of today's Pannonian Plain and was surrounded by the Alps, the Carpathians and the Dinarides. One of the most beautiful and richest fossil communities of the Pannonian Sea is preserved in Hum Zabočki at the Plavinka site. This place, where sand used to be mined, was neglected until it was arranged by kuburaši (firelock makers) of the Count Kulmer Association.

The sediments of the Plavinka geological site are about six million years old. A very rich community of fossil shells, snails, crabs and plants, about 60 species, was found in layers of sand, powder and clay. A bilingual educational and information board has been set up at the site, which talks about the origin, development and disappearance of the Pannonian Sea.