The Counts of Schwalenberg left the old castle Schwalenberg, which originally gave the family its name, later Oldenburg near Marienmünster, and built the city and the new castle, now known as Burg Schwalenberg. The castle was constructed from 1228 to 1231 during the time of Count Volkwin III. Around the same time, the town of Schwalenberg also emerged. The castle was pledged to various noble families from 1358 until the first quarter of the 17th century. In 1613, after the death of his father Simon VI., Hermann (1590–1620) inherited the office and the castle of Schwalenberg. He decreed that the keep be demolished in 1618. Later, it became the seat of branches of the House of Lippe. In 1627/28, a castle with elements of the late Renaissance was built on the site of the castle. One wing of the castle still remains, which was renovated between 1911 and 1913. Between 1938 and 1945, the castle was used as a convalescent home for mothers, and after that, it served as an evangelical children's recreation home until 1962. Subsequently, the building was renovated and converted into a hotel.
Situated on a hill above the town, the castle is accessible on foot or by vehicle from the city. The castle was sold in 2017, and as part of the planned redevelopment, it is undergoing renovations until 2019. The castle will be transformed into holiday apartments. These were approved in December 2018, and work on them has commenced. The castle cafe reopened in mid-January 2019.
References: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.