Päijälä hill fort is an Iron Age hill fort by the Lake Saaresjärvi in Kuhmoinen. The abundance of artefacts found at the Päijälä hill fort makes it nationally significant. The fort is thought to have been used since at least the 12th century. Kuhmoinen was then a borderland between Häme and Carelian tribes who fought over the ownership of wilderness areas.
The fort hill rises 25 metres above the surrounding terrain, and looking from above you can see the fort is built in a roughly circular form. The slopes of the hill are extremely steep from three sides.
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.