Saimaa is a glacial lake formed after the ice age and is the largest of 187.888 lakes in Finland. Located in southeastern Finland, Saimaa is connected with the Gulf of Finland by Saimaa Canal. In the city of Savonlinna, which is the main city of Finland lake area, lays the Olavinlinna castle. Popular spa and holiday resort, Savonlinna grew around Europe's northernmost medieval stone fortress which is standing since the 15th century. There are a Castle museum, Orthodox Museum and few other exhibitions in the castle, and it hosts the Savonlinna Opera Festival every summer since 1912.