A significant sight of Altenstadt, Schongau, is the Romanesque basilica minor of St. Michael with remains of medieval wall painting and several examples of Romanesque sculpture.
The basilica was built between 1180 and 1220 as the parish church of the settlement later known as Altenstadt in Upper Bavaria, Schongau. The late Romanesque building, made of tuff stone, has been almost entirely preserved or restored in its medieval form. The basilica is the only vaulted sacral building of the late Romanesque style in Bavaria. The most famous and significant artwork in the basilica is the 'Great God of Altenstadt.' The monumental 3.20-meter-high crucifix is flanked by depictions of Mary and John (copies, with the originals found in the Bavarian National Museum in Munich), situated on the modern rood screen above the choir entrance. The artwork dates back to the early 13th century. Instead of a crown of thorns, the Savior wears a gold band, depicting him as Christ the King.
In the choir and nave, several Romanesque and early Gothic frescoes have been preserved or uncovered. In the right (southern) side aisle, above the baptismal font, one can see the crucifixion, while in the choir, there is an image of the Archangel Michael as the weigher of souls and the Annunciation. On the inside of the west wall, during the renovation of the old organ in 1994, an eight-meter-high representation of Saint Christopher (circa 1200) was uncovered. The original baptismal font from the time of the church's construction has also been preserved. The chalice-shaped basin features reliefs of the Archangel Michael, the Madonna with Child, Saint John the Baptist, and the baptism of Jesus.
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.