It is believed that the hilltop Hartenstein castle was built by a possible descendant of the Kuenringer family, Heinricus de Hertinsteine, mentioned in records from 1187.
In the second half of the 17th century, the castle lords preferred more comfortable residences, abandoning Hartenstein to decay. Despite this, the castle withstood a brief siege by Swedish forces in 1645, who nevertheless destroyed an outer fortification. In 1726, Emperor Charles VI granted the estate to Baron Philipp Ferdinand von Gudenus, whose family retained it until 1927. From 1780 to 1799, Johann Heinrich von Gudenus used salvageable materials from the castle, such as doors and window frames, to build his hunting lodge, Els. By the early 19th century, the two towers were used as granaries. In 1892, Dr. Otto Pospischil leased the estate and converted the outer castle, rebuilt in a 'castle style' between 1892 and 1896, into a hydrotherapy facility. Meanwhile, the main castle had long fallen into ruin. During the Nazi era, the site served as a youth castle.
Below Hartenstein Castle lies the Gudenus Cave, eroded from the riverbank and inhabited by Neanderthals during the Stone Age. It holds the earliest settlement traces in Lower Austria, nearly 100,000 years old, including hand axes and other tools.
Stobi was an ancient town of Paeonia located near Gradsko. It is considered by many to be the most famous archaeological site in North Macedonia. Stobi was built where the Erigon (Crna River) joins the Axios (Vardar), making it strategically important as a center for both trade and warfare.
Stobi developed from a Paeonian settlement established in the Archaic period. It is believed that in 217 BCE, Philip V annexed Paionia during his campaign against the Dardani who had entered Bylazora, the largest Paeonian town.
The city was first mentioned in writing by the historian Livy, in connection with a victory of Philip V of Macedon over the Dardani in 197 BC. In 168 BC, the Romans defeated Perseus and Macedonia was divided into four nominally independent republics. In 148 BC, the four areas of Macedonia were brought together in a unified Roman province. In the reign of Augustus the city grew in size and population.