Kärnäkoski Fortress was part of a larger South-Eastern Finland fortification system built to protect Saint Petersburg, the capital of Russian Empire.

The construction of a large fortification system in south-eastern Finland was entrusted to general Alexander Suvorov.

The location allowed the fortress to guard the border between Sweden and Russia, control the traffic going via the road and monitor the shipping routes in western Saimaa.

The area near the fortress had been a site for several engagements between Swedish and Russian troops in the Russo-Swedish War that had just ended.

The less-vulnerable eastern and northern sides that were mostly protected by lake shore were defended only with tenailles.

Inside the fortress were built barracks, guardhouse, officers quarters, brig and gunpowder magazine.

As a result, the fortresses were disarmed, the buildings and remaining equipment were auctioned and the walls and fortifications were left untended.

Kärnäkoski fortress was built to protect against the Swedish threat, but never did see action against the intended enemy.

Other historical buildings nearby are an old barge harbor, mill and saw built in the 1830s and a double-arch stone bridge from 1886.