Thunstetten castle manor was built as a country manor house in the Bernese Oberaargau in 1711 to 1713 or 1713 to 1715. The castle was built for the Landvogt Hieronymus von Erlach following plans by the architect Joseph Abeille. The castle remained with the Erlach family until 1746. From 1746 until 1971 it had numerous owners. In 1971 the Stiftung Schloss Thunstetten (Thunstetten Castle Foundation) took over management of the building and grounds. Today rooms in the castle or the entire castle can be rented for events or meetings.
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.