The Ruhnu wooden church, built in 1644, is the oldest known wooden building in Estonia. The church's baroque-style tower was finished in 1755. The oldest parts of the building are the polygonal choir and altar, and the nave. The altar is covered with a thin, polished stone slate; the oaken frame stands on sand and is open towards the south.
The stone Lutheran church next to the wooden one was built in 1912 and is currently where services are held.
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.