The greystone church in Parainen was built in the 15th century (probably in 1440-1460) and is dedicated to St. Simon. The western part of the Agricola-chapel is the eldest component of the church, today a museum. On the churchyard is located the chapel of bishop Tengström, Finland's first archbishop (erected in 1819). The interior of the church is covered with several coat of arms. The rarest one is dedicated to pope Innocentius III.
National Board of Antiquities has named the church and the surrounding Vanha Malmi old town as national built heritage.
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.