Ruttenstein Castle was first time documented in 1209, in a deed issued by Duke Leopold for the Baumgartenberg Monastery, where it is mentioned under the name Rotenstein. The existing structure of the high castle, however, suggests that the castle is significantly older. The construction period likely falls in the first half of the 12th century, although this is not documented. It is probably a foundation of the Counts of Clam-Velburg.
The walls of the formerly massive pentagonal keep are now only partially preserved, tapering to a point and visibly towering over the site. The former residential wing in the west retains three of its walls. Above them, a viewing platform has been constructed, accessible via wooden stairs. Clearly recognizable, though also only partially preserved, is the early Gothic castle chapel located near the stone steps to the residential building. The main castle itself was protected on the north, south, and east by a mighty ring wall, which is still partially preserved today, and from which seven wall towers protruded.
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.