The colossal Heidenreichstein castle situated in the moorlands to the northwest of the Waldviertel is the largest and best preserved medieval water castle in Lower Austria. The oldest parts of the castle are dated back to the 12th century. It has never been in enemy hands since its construction. The walls of the four wings, the three corner turrets and the keep are up to four metres thick. A guided tour through the three-storey living apartments with spiral staircase and arcades discloses highly remarkable interior fittings including Gothic furniture, articles of daily life and portrait paintings.
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.