Opstainiai First Mound (Vilkyškiai)
It is the largest and most expressive hill in the regional park. The slopes of the hill are steep and high, reaching up to 20 m. It is near the town of Vilkyškės, well visible and accessible from the road Vilkyškis - Šereiklaukis. There are two ancient settlements adjacent to it where the skalvians lived between the first and the end of the thirteenth centuries, until this place was conquered by the Crusaders. The castle was built in a pop-up surrounded by the River Apsta. A cultural layer of 1.3 to 1.5 m was discovered on the eastern side of the hill. Studies have found particularly high levels of flammability, and it is believed that settlements have been burned repeatedly. Two, possibly specially equipped, fire brigades for the casting of bronze articles were also discovered. This is also evidenced by the discovery of casting moulds, parts of crucibles, and remnants of articles. Among the findings, there are many pot combs on a rough, polished, pinchy surface, spinns, pieces of plaster with markings of twins and logs, a knife, rubbing garden stones. These settlements are believed to have given way to the formation of the Vilkyškės town. The hill is known for its deliveries, which were written by E. Gizevijus back in the nineteenth century. The most famous of them about duchess Selmyte.