Vadstena Castle, Sweden

Vadstena Castle was originally built by King Gustav I in 1545 as a fortress to protect Stockholm from enemies approaching from the south. The fortress consisted of three smaller stone buildings facing Lake Vättern, three 31-meter wide ramparts, a courtyard, a moat and four circular cannon turrets. The original ramparts were torn down in the 19th century and the present ramparts were inaugurated in 1999. The stone buildings later formed the ground floor of the castle.