Turku Castle, located in Turku, Finland, is a medieval fortress that dates back to the late 13th century. It served as a bastion and administrative center in historical Finland until the early 19th century. The castle has undergone various renovations and restorations over the years, with its peak in the mid-16th century during the reign of Duke John of Finland and Catherine Jagellon. Today, it is one of Finland's most visited museums, attracting over 100,000 visitors annually. The castle features a mix of medieval and Renaissance architecture, including a keep and a bailey, and offers guided tours, a restaurant, and a souvenir shop within its walls.