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.
The ancient Argos Theater was built in 320 BC. and is located in Argos, Greece against Larissa Hill. Nearby from this site is Agora, Roman Odeon, and the Baths of Argos. The theater is one of the largest architectural developments in Greece and was renovated in ca 120 AD.
The Hellenistic theater at Argos is cut into the hillside of the Larisa, with 90 steps up a steep incline, forming a narrow rectilinear cavea. Among the largest theaters in Greece, it held about 20,000 spectators and is divided by two landings into three horizontal sections. Staircases further divide the cavea into four cunei, corresponding to the tribes of Argos A high wall was erected to prevent unauthorized access into the theatron and may have helped the acoustics, but it is said the sound quality is still very good today.
Around 120 CE, both theaters were renovated in the Roman style.