Photograph by Henriikka Vartiainen / Flickr, 2011,
licensed via CC BY-NC 2.0
Olavinlinna is a castle built in the 15th century,
located on a rocky island in the Kyrönsalmi strait, which connects the waters of Haukivesi and Pihlajavesi.
Sweden, Denmark, and Norway had formed the Kalmar Union in 1397.
It was decided to build a new castle on the border of the 1323 Treaty of Nöteborg
to improve protection against the threat posed by the Novgorod Republic and the Principality of Moscow.