Kyminlinna (literally, 'the castle of Kymi') is a fortress located in the northern part of island of Hovinsaari in Kotka, on the south coast of Finland.

Kyminlinna is part of the South-Eastern Finland fortification system built by Russia after the Russo-Swedish War of 1788-1790.

The fortress is surrounded by incomplete moats, which also form part of the ditch system intended to drain the grounds.

The construction of the fortress was initially supervised by the Russian Marshall Alexander Suvorov, later followed by the Dutch-born General Jan Pieter van Suchtelen.

The fortress was also used as a prisoner of war camp, tuberculosis hospital and civil guard firing range.