The sinkholes are in place Bakar hinterland where you can see the unique karst phenomenon called "Now it has, now he does not have a lake", which is pretty rare, not only in Croatia but also abroad. Specifically during exceptionally rainy periods catchment and groundwater from karst valleys create a lake and so Ponikve in just a few hours become a place by the lake. This phenomenon was short-lived because the water of the lake, but the first storm back into underground streams Bakar sources.