Gars am Kamp Castle was built around 1120-1130. The heterogeneously arranged complex of the hilltop castle stands on terraced land descending in three levels by the Kamp River.
On the highest level stands the main castle, enclosed by a ring wall. On the second, middle plateau, there are the southern gate tower and the castle chapel, a hall building from the 16th century to the west, and the surrounding fortifications from the 13th century. On the third, lowest level, connected by a castle path, the fortified outer bailey hosts the parish church of Thunau am Kamp on a southern terrace. A small coat of arms stone of the Rotthal family (dated 1709) is located above the portal to the north tower.
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.