Founded in 1280 at the mouth of the Aurajoki, mammoth Turku Castle is easily Finland’s largest fortress. Highlights include two dungeons and sumptuous banqueting halls, as well as a fascinating historical museum of medieval Turku in the castle’s Old Bailey. Models depict the castle's growth from a simple island fortress to a Renaissance palace. Guided tours in English run four to six times daily from June to August.

　　Swedish count Per Brahe ruled Finland from here in the 17th century, while Sweden’s deposed King Eric XIV was imprisoned in the castle’s round tower in the late 16th century. He was moved to several prisons, including Åland’s Kastelholms Slott, to prevent his discovery by rebels. Today most Finns recognise the castle's distinctive architecture as the logo for Turun Sinappi (Turku Mustard).