Koroistenniemi in Turku was Finland's key secular and ecclesiastic centre in the 1200s. According to a letter by Pope Gregory IX in 1229, the centre of the diocese of Finland, the bishop's see, was moved to Koroinen. Today, only the stone foundation of the church remains. Other buildings have stood on the headland in addition to the church. The ruins of a stone building, thought to have been the Bishop's palace, are the best preserved of these. To the east, Koroistenniemi is surrounded by a 100-metre wall and a dry moat in front. Behind them, the Koroinen estate, which belonged to the church, can be seen from the headland. To the east of the moat, evidence has been found of Iron Age settlements and a cemetery that are both older than the church.
A guided tour for groups subject to a charge is available by advance booking from the association Elävän kulttuurin Koroinen ry (www.koroinen.info, in Finnish). Advance registration is compulsory for groups.
The Koroinen main building café, run by the association Elävän kulttuurin Koroinen ry (www.koroinen.info, in Finnish), is open on Sundays throughout the year.