Oulu Castle was a late defense castle in Oulu, Finland. It was built on an island in the delta of Oulu River in 1590. The castle was mostly made of wood and earth walls. There probably was an earlier medieval castle on the same site latest by 1375. The Russian Sophia Chronicle has recorded that men from Novgorod tried to conquer a new castle in the Oulu River delta in 1377 but were unsuccessful.
The present-day ruins on the Linnansaari island remain from an even later castle, which was built in 1605 by order of King Charles IX. The king's power of attorney of April 8, 1605, first orders the construction of Kajaani Castle and then orders the rebuilding of Oulu Castle.
Wikipedia https://en.wikipedia.org/wiki/Oulu_Castle
Address (Unnamed Road), 90100, Finland
Coordinates 65°1'2.043" N 25°28'2.312" E