Vyborg Castle was one of the three major castles of Finland, the three being the castles of Turku (Åbo in Swedish) and Hämeenlinna (Tavastehus), and Vyborg (Viborg).
It was built as the easternmost outpost of the medieval Kingdom of Sweden: it is located on the Karelian Isthmus, on a little islet in the innermost corner of the Gulf of Finland, in a tight strait which connects Zashchitnaya Bay to Vyborg Bay.