The castle of Virtsu belonged to vassals of the feudal state Bishopric of Ösel-Wiek - Western part of nowadays Estonia as well as part of Saaremaa and part of Hiiumaa. It was built in 1430 by Uexküll noble family and destroyed already in 16th century. Now the ruined walls are few metres high, but it really looks that there is almost nothing. That's because grass and bush is growing on the ruins.
Reference: Virtual Tourist
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.