Kärnäkoski fortress was part of the South-Eastern Finland fortification system built by Russians in the 1790's. Purpose of the fortress was to protect the strategic road to St. Petersburg and Russians fleet in Saimaa against Swedish enemies from the west. Building was started in 1790 by French engineer officers and it's a tradional French bastion system. Approximately 1400 Russian soldiers and local peasants were forced to construction work and many of them died in hard work and illnesses.
Kärnäkoski protected the border only 15 years and after Finnish War in 1808-1809 fortress lost its defensive value. Kärnäkoski was disbanded in 1835 by the tsar Nicholas I. After that fortress was disarmed, buildings and remaining equipment were auctioned and the walls and fortifications were left untended. Kärnäkoski never took part to a military action, but in Finland Civil War (1918) several battles were fought nearby.
Today Kärnäkoski fortress is a tourist attraction, although there are no guided tours or other tourist or travel services in the fortress, simply guidance signs. Finnish National Board of Antiquities and Finnish Ministry of the Environment have listed the fortress area as nationally significant cultural historic landmark. NBA has restored Kärnäkoski fortress to its former shape together with other fortresses in south-eastern Finland. Walls were repaired and the fortress area was restored and cleared. Other historical buildings nearby are an old barge harbor, mill and saw built in 1830s and a double-arch stone bridge from 1886. The mill has not been used since 1950s, but was restored by a local village organization in 2002.
The city walls of Avila were built in the 11th century to protect the citizens from the Moors. They have been well maintained throughout the centuries and are now a major tourist attraction as well as a UNESCO World Heritage Site. Visitors can walk around about half of the length of the walls.
The layout of the city is an even quadrilateral with a perimeter of 2,516 m. Its walls, which consist in part of stones already used in earlier constructions, have an average thickness of 3 m. Access to the city is afforded by nine gates of different periods; twin 20 m high towers, linked by a semi-circular arch, flank the oldest ones, Puerta de San Vicente and Puerta del Alcázar.