The building is owned and maintained by the Finnish state and is entrusted to the use of the city of Turku. The castle functions in its entirety as a historical museum as part of the Turku provincial museum. In the main part of the castle are banquet rooms for the city of Turku, a church for the local congregation and also restaurants in both the main castle and the bailey. Today the castle is once more experiencing a heyday as it has achieved the status of being one of Finland's most visited museums. Construction The layout of the castle consists of the Medieval keep (päälinna) and Renaissance bailey (esilinna). The keep consists of a square fort with two square gateway towers whose wall thickness at the base is some . In the Middle Ages the castle was surrounded by a moat conjoining with the River Aura, the castle effectively lying on an island. The keep was completed in the early 15th century. Construction of the bailey was begun in the late 15th century and finished in the 16th. The bailey is not as heavily fortified as the keep, but it has several turrets. The Renaissance construction work included heavy modification of nearly all the rooms in the older medieval part of the castle. Since the Renaissance no additions have been made to the castle. The modest military fortification grew into a massive greystone castle, whose solid walls have witnessed many milestones in Nordic history. The castle has been subject to numerous sieges and several battles have been waged aside its walls. Of all Finnish castles, Turku castle has the most warlike history besides Vyborg castle and Olavinlinna. The castle's heyday was in the mid-16th century during the reign of Duke John of Finland and Catherine Jagellon. That was when the Renaissance Floor and King's and Queen's hall were built, along with other features. The castle was the center of the historical province of Finland Proper, and the administrative center of all of Finland. Its strong walls and dungeons also served as the state prison for centuries; even today, a prison is colloquially referred to as linna (castle) in Finnish. The castle has been the place of many historical events; in 1573–1579, for example, the deposed Swedish queen Karin Månsdotter was kept prisoner here. The castle is Finland's most visited museum, with attendance reaching 200,000 in some years. In addition, many