Hakoinen Castle (Hakoisten linnavuori in Finnish) is the ruins of a fortification on a hill in Janakkala, Finland. Dated to the medieval period, the fortification was situated on a very steep-sided rock by Lake Kernaala (Kernaalanjärvi) in a manner reminiscent of the hill fort tradition. The top of the rock is 63 metres (207 ft) above the water level of the lake. Today very little remains of the castle. Equally little is known about its origins. The castle was probably built at the end of the 13th century or in the early 14th century. It has been speculated that Hakoinen might have been the fort that was attacked by invading Novgorodian forces in 1311 during the Swedish-Novgorodian Wars, as described in the Novgorod Chronicle
According to excavations, the castle was divided into two parts. Lower defensive constructions were mostly made of wood. Constructions on the rock were of bricks and rocks. The castle probably had one tower.
