The remains of the castle can be visited
Mitterberg Castle

The castle ruin Mitterberg is located about 3 km east of the town of Perg on a rocky hill southwest of the settlement Mitterberg, which belongs to the cadastral community of Pergkirchen. A few hundred meters south of the ruin lies the village of Thurnhof.
In the 17th century, stones from the castle were used for the construction of Windhaag Castle and Pragtal Castle. Therefore, only parts of the curtain wall with round towers and a stump of the keep remain. Mitterberg was formerly the largest castle in the Mühlviertel and from 1278 to 1491 the seat of the great regional court of Machland.
In the Middle Ages, the fortress was the largest castle complex in the Mühlviertel and, after Schaunburg Castle (municipality of Hartkirchen), the second largest in the area of present-day Upper Austria.
The complex extends over a length of more than 200 meters and had three outer bailey in front of the main castle. A detailed description can be found on Martin Aigner's castle page.
During excavations on the site of the former castle, numerous ceramic fragments were uncovered, which are now in the collection of the Heimathaus Stadtmuseum Perg (Leopold Mayböck Collection).
Owners and Feudal Lords of the Mitterberg Dominion+
The name of the castle is first documented in 1165. The builders and first owners were most likely the Lords of Perg. It fell to the Babenberg sovereign at the latest after their extinction in 1191. The castle probably belonged to those estates that were confiscated by the Babenberg Duke Leopold V in 1180 and later again granted as a fief to Friedrich II of Perg. In 1208, Gumpold and Marquard von Mitterberg resided at the castle. A relationship with the Lords of Perg and Machland is rather unlikely.
Other noble families at Mitterberg included in particular the Kapeller, Wallseer, Zelkinger, and Prüschenk.
In 1277, Ulrich II von Kapellen received Mitterberg Castle as a princely fief from King Rudolf I, Duke of Austria, and a little later also the Machland regional court. In 1279, he became captain of the Enns region. Duke Albrecht I of Austria renewed the enfeoffment of the Kapeller. The regional court was pledged to the Lords of Kapellen in 1318 and 1386.
Hans I von Kapellen (also known as Janns von Capellen) built a Marian chapel in the inner courtyard of Mitterberg in 1351, in which context the parish of Pergkirchen had to be compensated with estates in Kreuzen and Mitterkirchen. The spiritual feudal lord of the parish church of Pergkirchen, the abbot of Melk Abbey, then granted the Kapeller a chaplain for their castle chapel.
Since one of the daughters of the last Kapeller (Eberhard II von Kapellen († 1406), Dorothea von Kapellen († around 1426)) married Hartneid V von Liechtenstein († 1427), Mitterberg initially passed to them and later to the Wallseer and Zelkinger, remaining in their possession until the end of the 15th century.
In 1491, a smaller part of the Mitterberg dominion, with the castle already partly dilapidated into a ruin, was separated from the Machland regional court and annexed to the newly created Windhaag regional court by Emperor Friedrich III, which at that time belonged to the Prager family. The larger part of the Mitterberg dominion and the regional court fell to the brothers Sigmund and Heinrich Prüschenk, the later Counts of Hardegg and in Machland. From 1491 to 1493, they had built Greinburg Castle, originally called Heinrichsburg. A caretaker remained in Mitterberg for the time being. Finally, the castle was completely abandoned and fell into increasing disrepair. Around 1560, parts of it were demolished.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Clemens Beutler (oder Beuttler) / Public domain via Wikimedia Commons
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 48.2532, 14.6588