Smlednik Castle was presumably built in the 12th century on the foundations of a prehistoric fort and a Roman stronghold of a later origin. The strategic location of the hill overlooking a crossing of the Sava River was appreciated by the first lords of the region, the Counts of Weimar Orlamunde, who built a defence tower on the hilltop in the 11th century. The tower was then expanded in several phases, but remained unaltered after 1610 and is thus the purest example of the architectural development of a mid-sized medieval castle in central Slovenia.
The famous Slovenian chronist Janez Vajkard Valvasor reffered to the Smlednik castle as a ruin already in the second half of the 17th century.
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.