The Kärnäkoski fortress is located on the Saimaa shore next to rapids that connects Saimaa and Kuolimo. It was built in 1791 as part of Russia’s outermost chain of fortifications against Sweden. The fortress was used to monitor water traffic between Lappeenranta and Savonlinna and road traffic along the Lappeenranta-Mikkeli road. There are fantastic views over labyrinthine Saimaa from the fortress.