The Altes Schloss or old castle, originally – since the 13th century – the heart of an extended hunting ground, surrounded by moats and equipped with numerous ancillary buildings, today forms an important visual motif in the gardens. It became a Habsburg possession in 1333 and was extended in the 17th century by Lodovico Burnacini.
After an attack by the Turks in 1683, this building was reconstructed in 1693 and another floor was added. Until World War I, together with the Blauer Hof, built in the 18th century, the Altes Schloss served as a spring residence for the Habsburgs.
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.