Built around 1250 by the lords of Berkule, Calenberg Castle was granted to the Papenheim family in 1307 and later became known as Rave von Calenberg. After a feud over inheritance in 1464, it was resolved in 1471. In 1868, Hugo Schuchard purchased the estate, including the castle, and extensively renovated it from 1880 to 1884. The castle served various purposes over the years, including housing refugees after 1945. In 1972, it was acquired by Karl-Heinz Rehkopf and faithfully restored.
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.