Hakoinen Castle (Hakoisten linnavuori in Finnish) are the ruins of a fortification on a hill in Janakkala, Finland. Dated medieval, the fortification was situated on a very steep rock by lake Kernaala (Kernaalanjärvi) reminiscent of a hill fort tradition. The top of the rock is 63 metres (207 ft) above the water level in the lake. Today very little remains of the castle. Equally little is known about its origins. One postulation is that it was built by the Swedes as their original stronghold in the medieval Häme area.