Koroinen was the residence of Bishop of Finland between years 1229 and 1300. in 1300 the bishop seat was moved couple of kilometres further down the River Aura, to the present-day Cathedral of Turku. There were at least two wooden churches in Koroinen built in the 14th century. The latest one was probably a stone church. It was later destroyed by the Victual Brothers in 1396.
Archaeologists have found remains of three wall grounds, which were probably part of the church. Today there are a white, wooden memorial cross and some stone foundations still remaining on site. The landscape of the site is anyway unique in Finland. You can see three medieval church from there: The Turku Cathedral, St Mary's Church and St. Catherine's Church.
The city walls of Avila were built in the 11th century to protect the citizens from the Moors. They have been well maintained throughout the centuries and are now a major tourist attraction as well as a UNESCO World Heritage Site. Visitors can walk around about half of the length of the walls.
The layout of the city is an even quadrilateral with a perimeter of 2,516 m. Its walls, which consist in part of stones already used in earlier constructions, have an average thickness of 3 m. Access to the city is afforded by nine gates of different periods; twin 20 m high towers, linked by a semi-circular arch, flank the oldest ones, Puerta de San Vicente and Puerta del Alcázar.