The name of Kostná Valley (The Bone Valley) is not random. It is an important locality of early Tertiary bones of tapirs, mastodons and rhinos. Kostná Valley is therefore of European importance.

Due to its uniqueness, Kostna Valley is a national natural monument. It is located in the Cerová Uplands Protected Landscape Area near the village of Hajnáčka.

The site was discovered in the 19th century, when Emil Ebeczky, a landowner, collected bone remains after the spring rains and founded a homeland museum.

On this site, bones or teeth of panda bear, hyena, primate, rodents, insectivores, birds, reptiles, amphibians, fish, and others have been found.

The area of almost 4.5 hectares is protected by the 4th level of protection. Rare bone findings have been preserved in very good quality due to the fact that there are still active volcanoes around Hajnáčka. Occasional volcanic activity created the character of the landscape.

Paleontological findings from this locality can be seen in the nearby Gemer - Malohont Museum in Rimavská Sobota, where one whole exhibition is dedicated exclusively to the Kostná Valley.