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 Broch of Clickimin is a large and well preserved, though somewhat restored broch near Lerwick. Originally built on an island in Clickimin Loch (now increased in size by silting and drainage), it was approached by a stone causeway. The water-level in the loch was reduced in 1874, leaving the broch high and dry. The broch is situated within a walled enclosure and, unusually for brochs, features a large 'blockhouse' between the opening in the enclosure and the broch itself. Another unusual feature is a stone slab featuring sculptured footprints, located in the causeway which approached the site. Situated across the loch is the Clickimin Leisure Centre.