Kuusisto Castle (Finnish: Kuusiston piispanlinna, Swedish: Kustö biskopsborg) was a medieval episcopal castle on the island of Kuusisto in Kaarina, Finland, near Turku. The castle was probably built in the early 14th century, although the site seems to have been a bishop's residence by the 1290s.
The castle was ordered to be demolished during the Protestant Reformation in 1528 by the king Gustav I of Sweden. Excavation and reconstruction work on the remaining ruins began in 1891.
Structures of Kuusisto Castle during the excavation in 1894
Kuusisto Castle ruins today
A room in ruins
Coordinates: 60°24′28″N 022°28′29″E / 60.40778°N 22.47472°E