Greinburg Castle was built between 1488 and 1495 by Heinrich and Siegmund Prüschenk with the imperial approval of Emperor Friedrich III. In 1533 Johann Leble (Löbl), acquired the castle. Under him the building received most of its present day form. In 1621 the castle was sold to the Earl Leonhard Helfrich of Meggau, who carried out basic changes. A three storeyed, columned arcade became the main feature for the appearance of the inner courtyard. Furthermore, under Meggau the Sala terrena (so-called stone theatre) was installed. In 1625 the “Rittersaal”, the Hall of Knights, and an adjoining chapel in the south west tower were redecorated.
The Dukes of Saxe-Coburg and Gotha have been owners of the Castle only since 1822. The building, which comprises four wings, houses the Coburg Rooms, which are the official rooms of the ducal family, as well as the Upper Austrian shipping museum.
The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.